Kanab, Utah, to Flagstaff, Arizona
0.0 Junction at Southeast End of Kanab, Utah. Head South on Alternate U.S. Highway 89 Toward Grand Canyon.
2.4 Junction of side road to the Kanab airport. To the south the wooded cuesta of Shinarump Sandstone forms the ridge separating the east-west trending subsequent valley carved on the Chinle Formation, over which we are riding, from the valley to the south which is cut in Moenkopi beds.
4.8 Utah-Arizona State Line. Entrance to a small refinery on the east side of the road. If the wind is right you get the aromatic smell of crude oil.
5.4 Entering Fredonia, a considerable distance north of where the built-up part of the town actually starts. The Moenkopi beds here form the Chocolate Cliffs, which extend both east and west (fig. 1.1). The Chocolate Cliffs are mappable westward toward Pipe Spring National Monument, where they are offset to the south along the major Sevier Fault. They then continue onto the west into the Arizona strip area.
6.6 Junction west to Colorado City and Pipe Springs National Monument, junction of Arizona Highway 389 with U.S. Highway 89. Continue on U.S. Highway 89A toward the south, around the bend and out of Fredonia. Ahead is the Kaibab Plateau, the prominent high structural block through which the Colorado River cut the Grand Canyon. The highway continues to the southeast over the red Moenkopi Formation for a considerable distance. Moenkopi redbeds have eroded to form the broad wide valley between here and the Kaibab Plateau (fig. 1.3).
12.3 Cross a small drainage through platy lower Moenkopi sandstone and siltstone.
12.6 Cross beneath the major power line from Page, and the Glen Canyon generating plant.
The highway crosses the base of the Moenkopi Formation and onto the Kaibab Limestone, here in very poor exposures. The flat stripped platform is typical of the top of the formation.
21.5 Guard rail in the drainage, base of the West Kaibab Monocline (fig. 1.4). Beyond the drainage is an explanatory sign of the Kaibab National Forest. The Kaibab Monocline rises to the south so that the same layers of rocks over which we are riding here form the surface on the uplands and the crest of the Kaibab Plateau on beyond.
Figure 1.1. Physiographic map of the southwestern part of the Colorado Plateau showing The Grand Staircase and the route of Guide Segment 1, around the southern margin of the High Plateau section and through the Grand Canyon section of the Colorado Plateau. C, Chocolate Cliffs; V, Vermilion Cliffs; W, White Cliffs; G, Grey Cliffs; and P, Pink Cliffs. (Modified from P. B. King, The Evolution of North America, Princeton University Press.)
4.5 Figure 1.2. Fredonia Rock, northeast from approximately Mile 4.5. Shinarump Sandstone caps the outlier, above the grey and reddish upper part of the Moenkopi Formation. The lighter rocks at the base of the bluff, below the letter F, are equivalent to the Shnabkaib Member of the Moenkopi Formation. Shinarump and Moenkopi beds form the Chocolate Cliffs east and west of the highway and separate the strike valleys carved on the easily eroded Chinle beds, to the north, and the Moenkopi beds, to the south.
Figure 1.3. Generalized columnar section of The Grand Staircase area extending from the Kaibab Plateau or the Marble Platform northward to the Pink Cliffs and Bryce Canyon National Monument. A. Generalized stratigraphic sections showing the principle rock units of the The Grand Staircase area. B. Regional geologic cross section showing the northward dip of the rocks off the Kaibab Monocline to beneath the Paunsagunt Plateau, and the relationship of the various cliffs formed by resistant Triassic, Jurassic, Cretaceous, and Tertiary beds. (Modified after P. B. King, The Evolution of North America, Princeton University Press.)
Figure 1.4. A generalized tectonic map showing structure in north central Arizona along the route of HW-89 Road Guide., from Kanab, Utah to Flagstaff, Arizona along U.S. Highway 89 and 89A. (Modified from Four Corners Geological Society Guidebook, 1969; and Kelley, 1955.)
22.1 Entering Kaibab National Forest. We begin to climb up the limb of the monocline through road cut exposures of the upper part of the Kaibab Limestone.
25.0 Forest Service Lookout Area. From here you can see the Grand Staircase area rising to the north over Mesozoic and Cenozoic rocks (figs. 1.3, 1.5). The Chocolate Cliffs of Shinarump and Moenkopi beds are overlain by the Vermilion Cliffs in upper
Figure 1.5. Aerial photograph looking northward from over the northern edge of the Kaibab Plateau, approximately at Mile 22, across The Grand Staircase to the Paunsagunt Plateau on the skyline. The first series of low cuestas are the Chocolate Cliffs (C), capped by resistant Shinarump Sandstone between the easily eroded Moenkopi and Chinle beds. The second series of cliffs are the Vermilion Cliffs (V), held up in large part by the Moenave and lower Navajo formations. The prominent light-colored cliffs on the skyline are the Pink Cliffs (P), held up by the Wasatch Formation. The latter unit has eroded to form the badlands-topography of Bryce Canyon National Park. The Grey Cliffs (G) between the Pink and the White cliffs (W) are not well developed but are some of the badland- forming units in the gray slope. (Photograph by W. K. Hamblin.)
Chinle and Moenave Formations. The White Cliffs beyond are in Navajo Sandstone, with the higher step of the Gray Cliffs in Cretaceous shale and sandstone. The Pink Cliffs of Lower Tertiary rocks cap the sequence and the top of the Paunsagunt Plateau (figs. 1.1, 1.5). The road to the south rises through pinyon and juniper woodland, now pretty much into the pinyon area.
31.2 The forest grades into one of Ponderosa pine (fig. 1.6), but geologically the highway is still staying about on the same beds near the top of the Kaibab Limestone.
36.0 Jacob Lake Junction. Arizona State Highway 67 leads south into Grand Canyon National Park and to the north edge of Grand Canyon. See HW-67 Road Guide. for a description of the geology into the north rim of Grand Canyon. It is closed during the winter. Turn east toward Flagstaff. From Jacob Lake east the road continues across the top of the Kaibab Limestone through Ponderosa pine forest.
Figure 1.6. Ponderosa pine forest in Kaibab National Forest, along U.S. Highway 89A at approximately Mile 31.
39.7 Fossiliferous "cannon balls" in the upper part of the Kaibab Limestone (fig. 1.7). Most of these small spherical concretions contain at least fragments of the sponge, Actinocoelia, in the center of them.
Figure 1.7. Cherry, fossiliferous, Kaibab Limestone exposed on the north side of the highway at approximately Mile 40. The light-colored spherical chert nodules contain fragments or complete specimens of the sponge, Actinocoelia. Excellent specimens can be obtained from the debris and road fill on the south side of the highway.
46.3 Double road cuts through the upper beds of the Kaibab Limestone. The resistant unit on the hillsides between the last stop and here is the very cherty "cannon ball" unit.
46.6 View Point. To the north is the East Kaibab Monocline (fig. 1.4). The Kaibab Limestone dips eastward beneath Moenkopi redbeds that make the broad sagebrush-covered flats of Houserock Valley (fig. 1.8). On to the east Chinle beds have slumped extensively. Most of the tossed angular blocks, midway up the Vermilion Cliffs are landslide masses that have been rotated and dropped by gliding in Chinle Shale. The cliffs expose red brown ledgy Moenave Formation, which is capped by the Navajo Sandstone that weathers to the angular jointed cliff at the top. The Paria Plateau surface, above, is on the Kayenta Sandstone.
47.1 Overlook in the middle part of the East Kaibab Monocline. To the southeast is the Marble Platform. It is held up by the Kaibab Limestone where that resistant unit becomes nearly flat-lying east of the monoclinal fold. The Echo Cliffs are on the skyline to the east. We'll later travel parallel to them on the east side of the Marble Platform practically from here to near Cameron, Arizona.
47.6 Lowermost Moenkopi redbeds in double road cuts on the switchback on the flank of the monocline.
48.0 Moenkopi rocks again exposed along the axes of a small syncline and very gentle anticline, on the flank of the East Kaibab Monocline.
48.9 Leaving Kaibab National Forest at the base of the monocline. Off to the south and the north the eastward-dipping Kaibab Limestone forms the resistant monoclinal surface but beneath the ranch, ahead, these same rocks are almost flat.
Figure 1.8. View northward from Mile 46.6 of rocks along the East Kaibab Monocline and Houserock Valley. The Kaibab Limestone is exposed in the foreground on the west side of Houserock Valley and is the resistant unit which expresses the monoclinal flexure. Houserock Valley is eroded along soft Moenkopi and Chinle beds. Younger Jurassic and Triassic rocks form the escarpment to the east of Houserock Valley.
49.4 Houserock Ranch, now pretty well abandoned. The highway now is on the northwest part of the Marble Platform, on top of the Kaibab Limestone. The platform extends southward from here into the Grand Canyon area.
51.5 To the north, against the Vermilion Cliffs, toreva blocks of Moenave and Navajo Sandstone have slumped down over the Chinle Formation. Purple and green Chinle Shale can be seen through the slumped blocks. The upper part of the cliff is made up of Navajo Sandstone, capped by a tongue of flaggy Kayenta Sandstone. Movement of the Chinle Formation, once the shale becomes wet, makes maintainance of roads across the Chinle Formation difficult. Roads can be easily constructed in the valley-forming sedimentary rocks but they later heave, producing hummocky uneven surfaces.
55.0 Side Road to South to Houserock Valley Wild Buffalo Ranch and the northern rim of the Colorado River gorge east of the monocline. U.S. Highway 89A from here eastward is on the lower part of the reddish Moenkopi Formation. Kaibab Limestone is exposed in areas to the south. The prominent butte on the skyline to the south is a remnant of Moenkopi Siltstone capped by Moenave Sandstone.
58.5 Small ridge crest opposite the promontory in the Vermilion Cliffs. To the north a thin, light gray Shinarump Formation is showing in the gray and purple green Chinle beds. Magnificent toreva blocks of Moenave Sandstone have moved down over Chinle Shale beneath the promontory (fig. 1.9). The cliffs are still capped by Navajo Sandstone with just a few feet of Kayenta Sandstone at the top.
Figure 1.9. Slump blocks of Chinle and Moenave formations north of the highway opposite Mile 59. The volcanic ash-bearing Chinle beds are structurally unsound when they are wet. Gliding of Chinle and Moenave beds have produced the hummocky slumped surface, beneath the massive ledges of sandstone. Light-colored, gypsiferous, middle Moenkopi beds are exposed in the immediate foreground and middle distance.
58.7 Double road cuts through basal beds of purple and green shale in the Moenkopi Formation. To the east the maintenance road descends into laminated siltstones and sandstones of the top of the lower red Moenkopi, at the east end of the cut, east of mile post 556.
60.9 Greenish beds in the upper part of the Moenkopi section are in the gypsiferous Shnabkaib Member equivalent.
61.5 Bright, light-colored, gray green Shinarump Sandstone is exposed near the base of the escarpment, to the north, beneath an alluvial brownish sandstone and the rather typical gray, maroon, to grayish purple shale of the Chinle Formation (fig. 1.10). Considerable rubble of landslide debris, from the prominent angular-weathering cliff of Navajo Sandstones and Moenave beds, has accumulated on Chinle Shale. To the south and southeast the gorge of the Colorado River is the prominent break through the Marble Platform in the middle of the valley.
Figure 1.10. Stratigraphic sequence exposed in the Vermilion Cliffs north of U.S. Highway 89A at approximately Mile 62. Light-colored beds in the foreground are in the middle part of the Moenkopi Formation. The light double ledges in the first ledge zone are the Shinarump Sandstone, which is overlain by the slope-forming upper part of the Chinle Formation. Well-bedded reddish units at the base of the cliff are in the Moenave Formation, and lower Navajo Sandstone caps the prominent Vermilion Cliffs. Landslide rubble covers much of the varicolored Chinle beds at the base of the Vermilion Cliffs.
64.0 Excellent exposures of light-colored Shinarump Sandstone above chocolate brown, laminated Moenkopi beds close to the road. The cliffs expose from Chinle Formation up through Kayenta Sandstone on the top. Far to the north in addition, upper beds of Navajo Sandstone have eroded to rounded beehives on top of the plateau. The Shinarump Formation continues as a resistant unit to the east and protects the Chocolate Cliffs in front of the Vermilion Cliffs (fig. 1.11).
67.3 Cliff Dwellers Lodge, here in spectacular Moenkopi exposures beneath the ledge of Shinarump Sandstone.
67.9 The gorge of Soap Creek, to the south of the road, exposes the top of the
Kaibab Limestone and the base of the Moenkopi Formation. Immediately east of the lodge, large boulders have fallen down from the massive sandstones on the cliff but are now protecting pedestals of soft Moenkopi beds beneath them (fig. 1.12).
72.8 The Vermilion Cliffs Lodge and Trading Post, built almost on the contact between the Kaibab Limestone and the overlying Moenkopi Formation. Tan Kaibab Limestone is cut by deeply entrenched gorges to the cast. To the northwest Moenkopi redbeds form the cliffs up to the Shinarump Conglomerate, which holds up the shoulder beneath the soft slope-forming Chinle beds. Angular-weathering Navajo Sandstone still forms the major cliffs on the skyline.
Figure 1.11. View northward along the Chocolate Cliffs, in the foreground, and the Vermilion Cliffs, along the skyline, from south of Cliff Dweller's Lodge at approximately Mile 65. The low country in the foreground is on the Moenkopi Formation. The Chocolate Cliffs are capped by the resistant Shinarump Sandstone. Moenave and lower Navajo beds form the Vermilion Cliffs and are capped here and there by light-colored erosional remnants of Navajo Sandstone. Large blocks in the foreground have been washed from the Vermilion and Chocolate cliffs by flash floods produced as a result of intense, summer thundershowers.
76.0 Marble Canyon Lodge.
76.1 Access Road to Glen Canyon National Recreation Area—Lee's Ferry to the north. The turnoff is almost at the contact of the Kaibab Limestone and the base of the Moenkopi Formation. See Scenic Loop Road Guide. for a description of the geology between here and Lee's Ferry. Continue on U.S. Highway 89A toward Flagstaff.
76.3 Northwest Abutment to the Navajo Bridge Over the Colorado River. The bridge was completed in 1928 and has an arched span 616 feet long (fig. 1.13). The center of the bridge is approximately 470 feet above the river. Toroweap and Coconino Formations are exposed in the deep inner gorge. Both bridge abutments are in cherty upper Kaibab Limestone. This chert is ragged and blotchy rather than the fossiliferous "cannon ball" type cherts seen near Jacob Lake. Beyond the bridge the highway swings south along the base of the Echo Cliffs, along the Echo Cliffs Monocline (figs. 1.1, 1.4), staying about on the Moenkopi-Kaibab contact for a while. Rock units in the Echo Cliffs, on the east side, are essentially the same as those in areas to the west.
Figure 1.12.
Figure 1.13. Erosional remnants near Cliff Dweller's Lodge. Blocks of resistant Shinarump Sandstone are protecting pedestals of more easily eroded Moenkopi beds. The Vermilion Cliffs form the skyline in the distance.
Navajo Bridge as seen from the Colorado River. Abutments of the bridge are in Kaibab Limestone. Ledges along the canyon bottom are in the Coconino and Toroweap formations. The bridge is approximately 470 feet above the river, at the center of the span. (Photograph by W. K. Hamblin.)
80.0 Navajo Springs Maintenance Station and Rest Area on the east side. On the skyline to the east Navajo and Kayenta sandstones are intensely jointed and have produced sharp needle like weathering features. Jointing is probably related to folding and minor faulting of the Echo Cliffs Monocline. South beyond the maintainance station, the stripped gray surface of the Marble Platform stands out above the gorge of the Colorado River and its tributaries. Chocolate brown, slope-forming Moenkopi Formation is capped by resistant Shinarump Sandstone which holds up the first cliff. The slope above is on relatively thick Chinle Shale and is overlain by Moenave and Navajo beds.
82.0 The highway crosses a small fault, downdropped to the northeast.
83.9 Narrow Bridge across Jackass Creek. The road drops from the base of the Moenkopi Formation onto the top of the Kaibab Limestone. The Kaibab Limestone is brown, ledgy, and lenticular but obviously is the resistant unit which holds up the top of the Marble Platform.
87.9 To the east the trenched gap through the crest of the Echo Cliffs is for the new U.S. Highway 89, from the Glen Canyon Dam area and Page, Arizona. That highway drops down through landslide blocks of Chinle and Moenave beds (fig. 1.14) to meet alternate U.S. Highway 89 at Bitter Springs. The notch is, in part, fault controlled.
90.1 Junction of Alternate U.S. Highway 89 with Main U.S. Highway 89 at Bitter Springs. Continue toward Flagstaff on U.S. Highway 89. To the west of the junction, Kaibab Limestone is exposed in the gullies. The highway to the south is more or less on alluvial fill on top of the Moenkopi Formation. Upper Chinle, Moenave, and Navajo formations form the Echo Cliffs to the east. The highway continues to the south from here, much of the way toward Cameron, in the subsequent valley carved on the combined Moenkopi and lower Chinle formations along the Echo Cliffs Mono-dine.
Figure 1.14. View toward the southeast from approximately Mile 88. Cliffs on the skyline are held up by Navajo and Moenave beds, above the slope zone formed on the Chinle Formation. Lower ledges above the alluvial plain are in the Moenkopi Formation. The irregular topography of the lower slopes is produced by slumping on the relatively easily eroded Moenkopi and Chinle beds. U.S. Highway 89 cuts through the notch along the skyline and descends through the slumped Chinle sequence to meet U.S. Highway 89A at Bitter Springs, 2 miles to the south.
91.8 Shinarump Conglomerate and tilted, slumped, toreva blocks of overlying Chinle beds are exposed east of the road at the base of the escarpment. Top of the Kaibab Limestone is well exposed in canyons and gullies to the west.
92.6 Cross Roundy or Tanner Creek Wash. To the east, Moenkopi and Chinle beds are well exposed. To the south of the gully crossing, the highway is essentially on the Moenkopi-Kaibab contact.
64.9 Kaibab Limestone exposed in cuts immediately west of the road. The road continues about on the contact on the top of the Kaibab.
96.7 Cross small alluvial fan that is veneered with very coarse limestone boulders produced by flash floods coming off the Marble Platform to the southwest. Light-colored sandstone, east across the floodplain of sandy Roundy Wash, marks the Moenkopi-Chinle boundary. Here there is a lower red mudstone, middle sandstone, and an upper red mudstone beneath the small ledges of the Shinarump Formation.
99.0 Leaving the upper beds of the Kaibab Limestone. The road now diagonals across the Moenkopi Formation which is a thick bedded, chocolate-colored, silty, laminated mudstone. It is broken in the cut by a small fault.
99.6 Moenkopi exposures are capped by resistant Shinarump Conglomerate which is tan and sandy, in contrast to the thin laminated brick red and reddish brown Moenkopi rocks (fig. 1.15).
101.1 Side roads leading up onto the Marble Platform show Moenkopi beds beneath a thin Shinarump Conglomerate and with some Kaibab Limestone exposed in the head waters of the gullies to the west.
103.0 On the Echo Cliffs to the east, the light-colored and striped tan and reddish brown sandstone is the Navajo Formation resting on the more dark reddish brown Kayenta and Moenave formations (fig. 1.16). Most of Cornfield Valley, between the road and the base of the cliff, is carved on the Chinle Formation because the Shinarump Conglomerate forms the cuesta a short distance to the west. Moenkopi beds are exposed in gullies beneath the Shinarump and form small subsequent valleys between the Shinarump cuesta and the main uplift on the Kaibab Limestone.
Figure 1.15. View northward along U.S. Highway 89 parallel to the Echo Cliffs Monocline at approximately Mile 99. Shinarump Sandstone forms the cuesta cap to the left of the road. Chinle Formation has eroded to produce the low Cornfield Valley. Banded ledge and slope units in the cliffs are in the Moenave Formation and are capped by the intensely jointed, light-colored Navajo Sandstone.
107.2 A small community to the west.
109.2 Trading Post at Cedar Ridge. The road continues in the Moenkopi Formation with Kaibab beds exposed along the monocline to the west and Chinle and younger formation making the Echo Cliffs to the east. The rocks are jointed, which allows local breakdown in the Echo Cliffs, so that there are gaps along the cliffs allowing access to the plateau surface to the east.
110.7 Excellent exposures of lower Moenkopi beds.
111.1 Double roadcuts through Moenkopi beds. Kaibab Limestone is exposed a short distance to the west of the road, and Shinarump Conglomerate forms the light-colored sandstone cuesta-cap to the east.
Figure 1.16. Northeastward to the Echo Cliffs from approximately Mile 100. Chinle beds are buried by valley fill in the foreground, but the upper part of the formation is exposed in the base of the bluff. Moenave Formation forms the two prominent, angular weathering, reddish brown ledges in the middle part of the escarpment. Lower Navajo Sandstone produces angular, resistant cliffs along the skyline and is overlain by a rounded light-colored upper Navajo Sandstone, above a thin, slope-forming Kayenta Formation.
111.5 Excellent exposures of uppermost Kaibab Limestone in the road cuts.
111.7 Nearly a full section of Moenkopi beds is exposed in bluffs to the east, although the beds are cut by a small fault (fig. 1.17). The highway continues on the lower part of the Moenkopi and uppermost Kaibab beds.
112.8 Double road cuts through uppermost Kaibab Limestone and transition beds into the lowermost Moenkopi beds. The highway continues beyond the road cuts essentially on the top of the Kaibab Limestone.
113.5 Excellent exposures of lower Chinle beds to the east.
114.6 Moenkopi and Shinarump formations exposed in road cuts and bridge abutment on the southwest side of the road.
Figure 1.17. Northeastward from U.S. Highway 89 at approximately Mile 111.7. The top of the Kaibab Limestone forms the stripped surface in the immediate foreground, below a nearly complete section of banded Moenkopi Formation which is exposed in vertical bluffs n the middle distance. Moenkopi beds are faulted and juxtaposed against light-colored Shinarump Sandstone n the middle distance. The Echo Cliffs are composed )principally of Moenave, Kayenta, and Navajo sandstone, here considerably jointed so that the normally very persistant cliffs are broken by a series of gaps.
115.1 Moenkopi beds beneath thin discontinuous Shinarump Sandstones.
116.6 The Gap Trading Post, school, and other facilities. The road through The Gap was, until recently, the main access route to the Glen Canyon Dam site and to Kaibito and other areas to the northeast.
117.6 Upper Chinle beds exposed well to the east beneath the angular-weathering Moenave unit which forms a prominent cuesta beneath the Navajo Sandstone.
119.5 Moenkopi and Kaibab beds exposed to the west in the gully. From here to near Cameron the road is uneven, even though this is a new roadbed. This is because of gypsum heaving and bentonite heaving within the Moenkopi and Chinle beds. The steep-sloping pediment gravel from the Kaibab surface to the west has veneered much of the Moenkopi and Chinle beds in the western part of the valley, but to the east, the upper part of the Chinle, Moenave, Kayenta and overlying Navajo formations show very well.
121.4 Chinle beds, exposed beneath terrace cover, here demonstrate that the Triassic shale is particularly susceptible to heaving, and makes poor road beds.
122.7 Five thousand feet elevation marker in the Petrified Forest Member of the Chinle. A thin igneous dike (fig. 1.18) cuts lower formations at the base of the cliff.
Figure 1.18. A thin basaltic dike (arrow) at the base of the escarpment forms a cockscomb in easily eroded Chinle beds at approximately Mile 122.7. Moenave Sandstone forms the overlying ledge-and-slope zone, beneath the massive Navajo Sandstone which is exposed along the crest of the Echo Cliffs.
125.6 Hidden Springs Roadside Rest Area. The road continues through the lower Chinle Formation with Moenkopi rocks exposed to the west. The type section of the Moenave Formation is near Moenave, to the southeast (fig. 1.19).
126.1 Excellent exposures of the Petrified Forest Member of the Chinle beneath the more evenly bedded, lacustrian appearing pinkish upper Owl Rock Member of the formation. Fossil wood is common in the Petrified Forest Member, and may cap buttes near the road. Collecting fossil wood is illegal on the reservations.
Figure 1.19. View southeastward toward the community of Moenave and the type locality of the formation, from near the Hidden Springs rest area at Mile 125.6. Cliffs in the distance are principally in Navajo Sandstone above the slope-forming Moenave Formation that caps the plateau surface toward the right. Badlands topography at the base of the escarpment, beyond Hamblin Wash and in the shadowed foreground, is on the Chinle Formation.
126.5 Excellent exposures of Shinarump Conglomerate in the west with some exposures of Moenkopi beds showing in the farther reaches of the canyon. Outcrops of the overlying Moenave Sandstone now begin to swing to the southeast around the southwestern edge of the Black Mesa Basin.
127.3 Junction of U.S. Highway 160 with U.S. Highway 89. Continue south on U.S. Highway 89 toward Cameron, Grand Canyon National Park, and Flagstaff. For a description of the geology along U.S. Highway 160 see HW-160 Road Guide..
130.9 Cross Moenkopi Wash. The type locality of the Moenkopi Formation is downstream near the confluence of the wash with the Little Colorado River. The rounded purplish hill to the southwest is Shadow or Ghost Mountain (fig. 1.20), one of the northernmost of the volcanos associated with the San Francisco Peak volcanic field. San Francisco Peak volcanos show as conical features on the skyline to the south. Humphreys Peak, elevation 12,670 feet, is the highest point in Arizona. Pinkish Owl Rock beds are exposed along the wash and in the bluff to the east. This member is the pinkish laminated unit above the ashey appearing Petrified Forest Member (fig. 1.21). The road continues to be hummocky because of shale heaving in the Chinle beds.
Figure 1.20. Southeastward to Shadow Mountain or Ghost Mountain from approximately Mile 132. Shadow Mountain is a volcanic cone and is one of the northernmost volcanic features of the San Francisco Peak field.
132.9 Double road cuts through Chinle beds. Meander or point-bar deposits are well shown in the lenticular units in the middle part of the road cut.
Figure 1.21. View northeastward in early morning light of the peculiar erosion remnants of the lower part of the Chinle Formation, at approximately Mile 135. This same unit erodes to form the Painted Desert to the east.
133.8 Cross Beneath Power Transmission Line. The Shadow Mountain volcano is the rounded hill to the west. Kaibab Limestone on the Coconino Plateau forms skyline exposures to the southwest. These are south and west of the East Kaibab Monocline and the Blue Mountain Monocline. The Ward Terrace is the western edge of the Moenkopi Plateau to the east, beyond the Painted Desert.
135.3 Excellent exposures of the lower bentonitic, barren, rounded hill-forming Petrified Forest Member of the Chinle Formation can be seen in the immediate vicinity of the road, but is particularly well exposed to the west. The reddish asphalt highway base here is produced by utilization of volcanic debris quarried for road metal in the San Francisco Peaks area.
137.1 Good exposures of the same lower Chinle beds. The stripped plateau to the southwest is on sandstone within the Moenkopi and the Shinarump formations.
138.7 Abandoned uranium mine in lower Chinle Sandstone, east of the road, was worked from 1955 to 1958.
139.4 Arizona Agricultural Products Inspection Station for southbound lane.
139.9 Double roadcuts through Shinarump Conglomerate. From here the road drops to the south down into Moenkopi beds.
140.5 Exposures of massive sandstone in Moenkopi Formation. These sandstones were deposited as barrier island or deltaic units and are exposed in canyons cut along tributaries to the Little Colorado River.
140.8 Excellent Moenkopi exposures.
140.9 North Abutment to the Bridge Over the Little Colorado River.
141.1 South Bridge Abutment, Entering Cameron, Arizona. South of Cameron, pinkish maroon mudstones and siltstones of the Moenkopi beds are well exposed in road cuts. Massive cliffs along the river are in Shinarump Conglomerate (fig. 1.22).
Figure 1.22. View eastward, upstream, along the Little Colorado River from the U.S. Highway 89 bridge near Cameron, Arizona, at Mile 141. Moenkopi rocks form the rocky rim of the inner gorge. In the far distance Chinle and younger rocks hold up the Ward Terrace, on the skyline.
142.1 Off to the west can be seen the distal tip of the long, thin, at one time very fluid Tappan basalt flow, one of several from the San Francisco Peaks volcanic field to the south. This basalt flowed down a stream valley for approximately 60 miles and then down the Little Colorado River gorge for 9 miles.
142.8 Road Junction of Arizona State Highway 64 West to Grand Canyon National Park. For a description of that route see HW-64 Road Guide..
143.8 Platy, cross-bedded Shinarump Sandstone in contact with Moenkopi Formation in road cuts. Shinarump beds show a great variety of sedimentary structures.
144.4 Excellent exposures of fluvial sandstone channel-fill or distributary sandstone channel-fills within the Moenkopi beds near the switchyard of the transmission lines.
145.0 Double roadcuts through Moenkopi beds. Some of the massive fluvial or barrier sandstone units are exposed to the southwest.
145.6 Cross beneath power transmission lines.
147.2 Pass through conglomeratic units down into the lower part of the Moenkopi Formation. The gray sagebrush-covered areas ahead are on Kaibab Limestone flexed up along the Black Point Monocline.
147.7 Excellent exposures of platy, tidal flat-type Moenkopi deposits along both sides of the road from here down to the river bottom.
148.4 Lower beds of the Moenkopi Formation, now upflexed along the toe of the Black Point Monocline.
149.0 Red exposures of the basal Moenkopi Formation at side roads. The road climbs immediately up the Black Point Monocline on top of the Kaibab Limestone. Moenkopi beds have been stripped away and the surface lowered to the more resistant carbonate units. The east-west trending Black Point Monocline runs toward the west where it meets the Gray Mountain or Coconino Monocline which has a north-south trend in this segment. This latter monocline ends to the north in the major East Kaibab Monoclinal complex that heads westward into the national park area. Here, then, we see a whole series of rectangularly joined, somewhat crossing monoclinal flexures, with structural relief of up to 2,000 feet.
150.5 Boundary of Navajo Indian Reservation.
151.3 Gray Mountain Trading Post and Community of Gray Mountain. To the south, the myriad of small volcanos clustered around the main volcanic peak center can be seen both east and west of the road (fig. 1.23).
152.5 The road now is on gently southward dipping lower reddish beds of the Moenkopi Formation on the flat table like upland south of the Black Point Monocline.
Figure 1.23. View westward from approximately Mile 150 to the eastern end of the Coconino Plateau where Kaibab and Toroweap beds are sharply folded along the Grey Mountain Monocline. The flat platform in the foreground is held up by the same beds that cap the Coconino Plateau.
154.4 Black basaltic flows rest unconformably upon reddish Moenkopi beds. These are the northernmost, nearly continuous sheets of basalt related to the San Francisco Peak field. From here to near Flagstaff, the highway is built primarily across volcanic rocks.
156.1 Wauneta Trading Post.
157.5 Reddish exposures here and in the canyon to the southeast are Moenkopi beds capped by dark Black Point basaltic flows, related to eruptions to the south.
158.4 Basaltic boulder rubble on both sides is part of the major Black Point basalt. Pressure ridges and other small spatter-related structures show particularly well to the southwest.
162.7 Hanks Trading Post. Volcanic tephra cones show very well to the west.
164.0 Junction of Park Access Road to Wupatki National Monument and Sunset Crater Loop to the east. For a description of this side road loop see HW-395 Road Guide.. All of the countryside in the immediate vicinity is floored by basalt which issued from the fields to the south and southwest.
166.5 Trading post and lumber yard near electricity transmission lines.
167.3 Entering Coconino National Forest.
168.2 Mature basalt topography, both east and west of the road.
168.3 Quarry in tephra on the west side, at the base of a small volcanic cone.
168.8 Elevation 6,000 feet.
170.8 Entering Coconino National Forest, San Francisco Peak Section. The San Francisco Peaks are the high prominent peaks to the south. Humphreys Peak is on the west and Doyle Peak is on the east.
174.9 Side roads leading both east and west. To the east is O'Leary Peak, a volcanic cone now capped with a fire lookout tower (fig. 1.24). We're at the northern margin of the main San Francisco Peak volcanic field, with both basaltic and intermediate flows. Basaltic tephra tends to form rather low, black to dark brown-appearing cones, and intermediate composition lavas form slightly higher, more angular, lighter gray peaks (fig. 1.25).
Figure 1.24. View southeastward from approximately Mile 155 to volcanic tephra cones in the northern part of the San Francisco Volcanic field. Angular pressure ridges in the foreground are on basalt flows.
Figure 1.25. View south from approximately Mile 164 toward the San Francisco Peak volcanic field. Mt. Humphreys is the high, snow-capped peak on the skyline. It is the highest point in the state of Arizona, with an elevation of 12,670 feet.
177.3 Well-developed Ponderosa pine forest is growing on basaltic debris washed from the cones to the southwest.
179.0 Junction of Park Access Road East to Sunset Crater National Monument.
For a description of this loop road see HW-395 Road Guide.. Sunset Crater is the high cone with a pinkish top, visible now and then through the trees and due east down the road.
180.8 Basaltic spatter in the road cuts on the north.
184.3 Black Bill Park. U.S. Geological Survey personnel blew craters in an area of cinders to the right, out of view, to simulate the lunar surface as a training area for the Apollo moon landing crews.
188.1 Devonian Martin Formation, Mississippian Redwall Limestone, Pennsylvanian-Permian Supai Formation, Permian Coconino-Toroweap Formation and Kaibab Limestone are exposed west of the highway, on the east flank of Mount Elden. These Paleozoic units were uplifted during emplacement of the Mount Elden dacite.
189.5 Entering Flagstaff.
191.3 Pass Beneath Interstate 40 Interchange with U.S. Highway 89 Within Flagstaff. End of HW-89 Road Guide.. See I-40 Road Guide. for description of the geology east along Interstate Highway 40 to Albuquerque.
from Field Guide: Northern Colorado Plateau by J. Keith Rigby - Purchase Information
