Four Corners and Navajo Reservation
0.0 Junction of U.S. Highways 160 and 89. HW-160 Road Guide. follows U.S. Highway 160 east toward Tuba City and Kayenta. U.S. Highway 89 leads south toward the entrance to Grand Canyon National Park and Flagstaff. For a route description along U.S. Highway 89 northward or southward from here see HW-89c Road Guide.. The road junction is in the Petrified Forest Member of the Chinle Formation. The member is composed of interbedded stream-channel sandstone and varicolored shale and mudstone. This member erodes moderately easily and forms the strike valley to the north and south. From here the route of this guide leads upsection into younger and younger beds of the Chinle Formation.
0.7 Cross Hamblin Wash and rise from the Petrified Forest Member into the pinkish banded Owl Rock Member of the Chinle Formation (fig. 2.1). The upper member forms pronounced laminated pinkish gray and green badlands, distinctly unlike the rounded Painted Desert-type massive badlands of the underlying member.
1.6 Road rises up through the upper part of the Chinle Formation, a typical wavy to hummocky road. Highway construction is easy across the slope-forming parts of the formation, but holding the road after construction is difficult because the soft volcanic ash-bearing shales heave under load or after wetting and drying. Ashy gray marls and pinkish mudstones show well in badlands along the road. To the north the monocline along the Echo Cliffs separates the Marble Platform on the west from the Kaibito Plateau on the east. Hamblin Wash has eroded along the outcrop of the Chinle and Moenkopi formations between the more resistant Kaibab Limestone below and the cliff-forming Moenave and Navajo sandstones above.
Figure 2.1. View northward along east-dipping Chinle beds where the highway crosses the bluff immediately east of Hamblin Wash, at approximately Mile 1.5.
4.8 Side road north to Moenave. Approximately 500 yards north of the highway, along the Moenave road, three-toed dinosaur footprints (fig. 2.2) are preserved in one of the resistant sandstone beds of the upper part of the Chinle Formation. The tracks are in a barren area immediately west of the road. Local women may have exhibits of juniper seed and glass beadwork for sale at the site. Moenave is the community to the north near the tall poplar trees and spring areas along the Moenave Sandstone escarpment.
Figure 2.2. Three-toed dinosaur tracks exposed in a resistant sandstone approximately 0.5 miles north of the highway at Mile 4.8.
6.4 U.S. Highway 160 climbs through double road cuts in the almost Moenkopi looking upper part of the Chinle Formation in the candy-striped gypsiferous upper part of the section. Moenave beds hold up the escarpment to the north (fig. 2.3).
9.6 The highway now swings northward up off the floodplain of Moenkopi Wash through road cuts of Moeave Formation. These resistant sandstone beds form the plateau surface beneath the south end of Tuba City.
10.4 Junction of Access Road North to Tuba City and South to Moenkopi with U.S. Highway 160.
Figure 2.3. View northward to the Moenave-capped cliff of upper Chinle beds along the north walls of Moenkopi Wash, southwest of Tuba City, at approximately Mile 8.
11.7 Small reservoir east of Tuba City. Cross-bedded Kayenta Sandstone rests on top of the resistant Moenave Sandstone near the road. The road east of Tuba City is in poor exposures of Wingate-Kayenta-Navajo Sandstone blanketed by loose drifting sand. Castle Butte to the north and Middle Mesa to the northeast show Navajo Sandstone capped by Carmel Formation.
16.4 Now abandoned uranium processing plant and associated housing. Rounded Navajo Sandstone begins to show in exposures in Moenkopi Wash to the south. Brownish beds in the immediate vicinity are probably basal Carmel Formation.
25.6 Rest area at the western base of Middle Mesa. Navajo Sandstone forms the lower, light tan, rounded bluffs, (fig. 2.4) and are capped by flat-bedded reddish Carmel Formation which is overlain by remnants of Entrada Sandstone at the top of the mesa.
33.3 Side Road to Tonalea School. A short distance beyond the junction the road dips down into a wash which exposes upper Navajo Sandstone, crinkly reddish Carmel Formation, and reddish brown to grayish green Entrada Formation. Red Lake Trading Post is on the western bluff of the wash south of the highway. Reddish beds of the Entrada Formation have a mottled to marbled weathered surface. Red Lake is in the valley to the south.
Figure 2.4. View eastward from Mile 25.6 to massive, cross-bedded, Navajo Sandstone at the west base of Middle Mesa on the Hopi Indian Reservation. Well-bedded Carmel and the basal part of the Entrada Formation form the exposures on the skyline.
34.8 Elephant's Feet Rest Area. The "feet" are erosional remnants of light gray cross-bedded Entrada Sandstone (fig. 2.5). The "toes" are in the underlying reddish part of the formation. To the east Morrison Formation and Dakota Sandstone are exposed along the western end of Black Mesa.
39.7 Junction of side road to Navajo National Monument, Inscription House, and Navajo Mountain. U.S. Highway 160 swings parallel to the electric railroad right-of-way. The railroad hauls coal from Black Mesa to the Navajo Power Plant near Page, Arizona.
43.2 Cow Springs Trading Post. The prominent white sandstone to the south of the trading post is the Cow Springs Sandstone and is above the reddish part of the Entrada Formation and below the Morrison Formation. Prominent gray shales near the top of the mesa expose Mancos Shale capped by the coal-bearing Cretaceous Mesa Verde Group.
View southeastward of the two Elephant's Feet at Mile 34.8. These are erosionally isolated outliers of the Entrada Formation, which also forms the bluffs in the background to the right.
47.8 Coconino County—Navajo County Boundary. The Cow Springs Sandstone forms the relatively prominent light gray ledges to the south beneath Morrison beds (fig. 2.6). Morrison Formation forms the lower half of the Black Mesa escarpment and Mancos Shale and Mesa Verde beds the upper half. From high points along the road Navajo Mountain is visible toward the north. Navajo Mountain is cored by a laccolith, like intrusions in the Henry Mountains, La Sal Mountains, and Ute Mountain, but Navajo Mountain is still roofed with uparched Navajo Sandstone.
51.4 Junction of Arizona State Highway 98 with U.S. Highway 160. Arizona Highway 98 leads northwestward toward Page. To the south the front of Black Mesa still exposes Morrison beds as the gray and pinkish units near the base with Mesa Verde Sandstone forming the mesa cap. U.S. Highway 160 continues on through Klethla Valley which is carved on nonresistant Carmel and Entrada beds, south of the Organ Rock Monocline (fig. 2.7).
Figure 2.6. View southeastward from Mile 44 to the massive Cow Springs Sandstone in the Morrison Formation beyond the hogan. The upper slope and ledge zone is on Cretaceous sandstone and shale at the northern rim of Black Mesa.
63.6 Storage Silos and Tipple at the End of the Railroad (fig. 2.8). Coal is transported from the mines on the mesa to the southeast to the loading area by a belt system which is bridged over the highway. Coal in the strip mines area is up to 36 feet thick and as much as 100 feet of overburden is being removed in the mining operations.
64.4 Road Junction to Navajo National Monument Toward the North. See HW-564 Road Guide. for a description of the route to Betatakin Monument. A side road also leads south from here approximately 15 miles into the Peabody coal mine area on top of Black Mesa. Morrison and overlying Cretaceous rocks are exposed along the access road in the mesa front.
East of the junction there is a double series of cliffs on the escarpment. Lower ones are held up by Morrison Formation above the light gray Cow Springs Sandstone and the upper one is held up by sandstone of the Mesa Verde Group, above the gray Mancos Shale slope. 66.2 Rest Area. Massive very light gray Cow Spring Sandstone is exposed at the base of the mesa scarp and is overlain by reddish shale and light cliff-forming sandstone of the Morrison Formation. Behind the frontal lower cliff zone of Morrison Formation Mesa Verde rocks are exposed in the prominent banded cliffs on the skyline. Toward the north Navajo Sandstone and older units are exposed on the south end of Organ Rock Monocline at the northern edge of the Black Mesa Basin.
69.3 Massive slick rock exposures to the north are the top of the Navajo Sandstone dipping southward on the monocline. Klethla Valley through here is a subsequent valley in Carmel and Entrada beds.
72.6 Tsegi Trading Post. The highway is constructed across fill and debris from the escarpment to the south and across soft Entrada and Carmel beds (fig. 2.9). Massive Navajo Sandstone, slope-forming Kayenta Sandstone, and cliff-forming Wingate Sandstone are visible in canyons to the northwest where erosion has cut down into the still older Chinle beds along the Organ Rock Monocline in Tsegi Canyon (fig. 2.10).
73.5 Road cuts are in upper Navajo Sandstone along the narrows of Laguna Creek. Notice how deeply Laguna Creek has entrenched into the Recent sand and silt which partially filled the gorge.
76.2 The Organ Rock Monocline now swings to the north away from the highway. Road cuts are in Morrison Formation. To the north Navajo, Kayenta, and Wingate sandstones form spectacular flatirons on the monocline. To the south the Morrison Formation is now composed of massive series of channel-fill sandstone lenses. It is these kinds of deposits which have produced dinosaurs in various parts of the West. Uranium minerals have also accumulated in these kinds of rocks. Cretaceous rocks form the rim beyond on the skyline around Black Mesa Basin.
Figure 2.7. Generalized tectonic map showing the structures along and adjacent to Geologic Guide Segment 2, from U.S. Highway 89, in the west, to U.S. Highway 666, in the east (modified from Kelly, 1955). The route leads across the Four Corners area, north of the Black Mesa Basin and Defiance Uplift but south of the Monument Uplift. Abbreviations for the monoclinal flexures are as follows: CO, Comb Ridge; 0, Organ Rock; R, Rattle Snake; RL, Red Lake; CS, Cow Springs; RR, Red Rock. Laccolithic intrusions are shown: A, Abajo; C, Carrizo; U, Ute Mountain. Dashed lines indicate boundaries of major uplifts.
Figure 2.8. Storage facilities at Mile 63.6 at the terminus of a conveyor belt delivery system for the Black Mesa coal mine.
Figure 2.9. View northward up Tsegi Canyon at approximately Mile 72.5. The flat valley is blanketed with alluvium into which the creek is now deeply entrenched. Lowest exposures in the canyon are in the Chinle Formation, which is overlain by a cliff-forming Wingate Sandstone. The high promontory on the right is held up by jointed Navajo Sandstone. The rocks are dipping steeply to the south along the Organ Rock Monocline.
80.0 Double road cuts through sandstone in the Morrison Formation. Numerous small channels are cut into the sandstone, some of them are partially filled with green and red mudstones and others are filled with coarse-grained sandstone. Toward the north Agathlan or Agathle's Needle rises above the cuesta of Navajo Sandstone and older rocks beyond the town of Kayenta.
Figure 2.10. Northeastward at the Tsegi Trading Post. Navajo and Kayenta beds are dipping steeply to the south along the Organ Rock Monocline. The valley in the foreground, beneath the road is on the Carmel Formation. Cross-bedded Navajo Sandstone is exposed immediately north of the road.
84.2 Junction of U.S. Highway 163 and 160 at the South End of Kayenta. Continue east on U.S. Highway 160 towards the Four Corners area, past the Kayenta airport. The road here is on the easily eroded upper beds of the Jurassic section. To the north, Agathle's Needle and other small intrusions show both north and south of the Comb Ridge Monocline (fig. 2.11) cuesta which is held up by Navajo, Kayenta and Wingate beds.
85.2 To the east the road passes through blow sand and low-dune fields. The sand here has a peculiar greenish cast, probably related to a volcanic origin, as well as to erosion of the overlying Morrison and Mancos beds. To the north, on the horizon west of Agathlan or Agathle's Needle, Owl Rock stands as an outlier of Wingate Sandstone above Chinle beds.
Figure 2.11. View southeastward from approximately Mile 80 of the northeastern edge of Black Mesa. Mesa Verde Sandstone caps the escarpment above a slope zone on Mancos Shale. Morrison beds form the prominent lower cliff and extend into the foreground area as well.
88.8 Prominent bluffs to the south are held up by the Cow Springs Sandstone in the Morrison Formation, above the Summerville-Entrada valley through which we are passing.
89.8 Top of the Navajo Sandstone, here blanketed by Recent pink windblown sand dunes.
91.2 Cross the wash. Church Rock, a volcanic diatreme, is to the north (fig. 2.12). This intrusion is one of a series of volcanic necks and dikes that extend from Agathle' s Needle southeastward to beyond Shiprock.
91.5 The road now climbs up over Cow Springs Sandstone and onto the base of the Morrison shaley beds. To the north a dike cuts southeastward from Church Rocks into the Morrison beds.
92.1 Side road junction to Rough Rocks. The flat mesa surface here and to the southeast is on Baby Rocks Mesa. Prominent flatirons of Navajo and Wingate sandstone on Comb Ridge to the north, separate Black Mesa Basin, on the south, from the Monument Upwarp, on the north.
Figure 2.12. Church Rock, a volcanic intrusion, north of the highway at Mile 91.2. The intrusion is in poorly exposed Jurassic beds above the Navajo Sandstone.
94.0 The road descends from the mesa surface through poor exposures of Morrison Formation, although Morrison Sandstone caps the mesa to the south and the east as well. Entrada and Summerville beds form the nearly vertical wall beneath the slope-forming Morrison.
96.9 "Stone babies" of the Entrada Formation now begin to appear at the base of the cliff to the south (fig. 2.13). The Comb Ridge Monocline, around the south edge of the Monument Upwarp, is still expressed in flatirons of Navajo Sandstone and older beds to the north.
Figure 2.13. View eastward from approximately Mile 97 of the jointed "stone babies" of the Entrada Formation at the north edge of Baby Rocks Mesa.
98.2 Baby Rocks Trading Post. The unusual weathering of the Entrada beds here (fig. 2.14), is partially controlled by joints, but also by irregularities in massiveness of the argillaceous and dolomitic siltstone. Morrison beds cap Baby Rocks Mesa. The Comb Ridge Monocline continues to the north of broad Laguna Creek Valley which is eroded principally on Carmel and Entrada beds.
Figure 2.14. Erosional remnants of the irregularly weathering upper Entrada beds west of Baby Rocks Trading Post, at the north edge of Baby Rocks Mesa. The slope above the escarpment, to the left, is on the basal part of the Morrison and the Summerville formations.
99.2 Navajo County-Apache County Line.
102.4 To the southeast the "stone baby" beds of the Entrada Formation form the complexly jointed and weathered cliff base, with Summerville beds, above, forming the more castellate cliff. The crest of the mesa is still cappcd by Morrison beds. The highway is in the lower part of the Entrada or uppermost beds of the Carmel Formation. Carmel Formation is exposed in the basal bedded unit of the northern promontory of northeastern Baby Rocks Mesa at road level.
103.6 Pass beneath a power line. The road descends onto the dune-capped floodplain of Laguna Creek. The main creek is to the north.
106.3 Junction primitive road to Navajo homes south and north. Cross-bedded Navajo Sandstone is exposed in low bluffs to the south and the north and is capped by a resistant unit of the basal Carmel Formation.
107.1 Cross-bedded Navajo Sandstone is exposed in road cuts in bluffs both to the south and the north at the divide.
109.2 Side road to Dennehotso to the North. The village is along Laguna Creek. Power poles and side roads to the south are in Navajo Sandstone, here with an upper reddish unit above the white unit visible to the north.
110.7 Prominent caliche-cemented gravel terrace above Navajo Sandstone on the south, near the rest area.
111.0 Cross Laguna Creek with Navajo Sandstone exposed north and south of the highway along the creek (fig. 2.15).
Figure 2.15. View southeastward of cross-bedded Navajo Sandstone at Mile 11.5.
112.2 Road in Navajo Sandstone but Carmel, Entrada, Summerville, and Morrison beds are exposed in the prominent butte on the north. Road cuts are through cross-bedded Navajo Sandstone in the belt where the formation is exposed around the northeastern margin of Black Mesa Basin.
113.7 Top of the Navajo Sandstone-base of the Carmel Formation. The latter formation is the horizontally bedded, reddish, alternating slope-and-ledge sandstone unit. The road climbs to the pass in the lower part of the Carmel beds. On to the north, around the bend, additional upper beds of the Carmel and lower Entrada formations are exposed. Carrizo Mountains are the flat-topped peaks in the distance, far to the southeast, with the Chuska Mountains as the high point farther to the south, beyond the extensively exposed Navajo Sandstone. Cretaceous rocks of the eastern rim of Black Mesa Basin shows to the south and southwest.
115.8 White rocks to the north are Navajo Sandstone dipping southward off a minor anticlinal structure.
117.1 Shallow double road cuts through basal Carmel Formation down onto cross-bedded Navajo Sandstone which forms the "slickrock" along the canyon to the south and in the bluffs to the north.
118.8 Side road to a hogan and a lookout area above the flat-bottomed arroyo of Chinle Creek, here entrenched into Navajo Sandstone (fig. 2.16). Bluffs of Navajo Sandstone rise above the flat valley floor which has been further cut by recent flooding.
119.6 Road descends to Chinle Creek Valley through double road cuts in the Navajo Sandstone.
120.0 Cross Chinle Wash at Tes Nes Iah, a new motel complex. Eastward the highway climbs up off the floodplain through double road cuts of Navajo Sandstone and continues eastward on Navajo Sandstone.
Figure 2.16. View south from Mile 118.8 to Chinle Wash over cross-bedded Navajo Sandstone. Chinle Wash is entrenching into more recent alluvial fill. Navajo Sandstone also forms the cliffs in the undercut slope of the meander in the background.
123.3 Reservation roads to the south and north are still on Navajo Sandstone.
124.0 Cross beneath electricity transmission line. The highway is through excellently exposed, cross-bedded Navajo Sandstone blanketed with extensive modern dune fields, partially trapped by vegetation.
125.8 Junction of Arizona State Highway 63 With U.S. Highway 180. State Highway 63 leads south to Chinle, Many Farms, and other communities along the east side of Black Mesa Basin. U.S. Highway 180 continues eastward through Navajo Sandstone.
126.2 Cross Walker Creek and Enter into Mexican Water, a trading post-restaurant community. Watch for burros and mules on the road. U.S. Highway 180 continues east through eolian cross-bedded Navajo Sandstone, with some minor interbedded fluvial beds.
128.9 The irregular hills beyond the power line to the north are capped by volcanic debris which rests on Morrison and older beds along the bluffs. This is part of a series of volcanic exposures extending northwesterly from the north end of the Carrizo Mountains.
130.5 Cross beneath power transmission poles. The white sandstone sequence on the north is basal Morrison Formation. Older rocks below are in the Carmel-Entrada section. The irregular points on the hills to the north and east are volcanic rocks.
131.7 Double road cuts through Morrison Formation at the pass.
132.7 Volcanic rocks to the south and to the north of the highway (fig. 2.17).
Figure 2.17. Southeastward to a ridge held up by volcanic debris. The ridge is part of a volcanic pile which extends northwestward from the Carrizo Mountains. The power transmissions lines lead westward from the Four Corners generating plant in the San Juan Basin.
135.5 Crest of the hill. The prominent butte to the south is capped by volcanic rocks on top of Morrison beds. The double road cuts to the east are through Morrison sandstone and shale.
139.3 Red Mesa Public School on the North. Red Mesa, beyond the school to the north, is held up by a Morrison cap above Summerville and Entrada beds.
140.8 Red Mesa Trading Post on the north. Tanks of the Red Mesa oil field are visible on the skyline to the north.
141.0 Junction of road to Aneth and a more primitive road south along the west side of the Carrizo Mountains with U.S. Highway 180. Volcanic flows cap light-colored ash beds that are exposed along the north side of the Toh-Atin Mesa above Cretaceous rocks.
143.4 Bend in the road toward the north. Possible evaporite heaving is expressed in upper Entrada beds beneath the light-colored Morrison Sandstone.
143.9 Road cuts through Morrison Sandstone.
144.4 Side road south to Sweetwater (14 miles). The older Entrada beds exposed near Red Mesa are on the crest of an anticlinal structure and rise above the general Morrison countryside which here extends far north and south of the road.
147.7 Cross beneath a transmission line leading westward from the Four Corners plant. Black Rock Point in the Carrizo Mountains to the south is capped by volcanic rocks above a Cretaceous sequence. Pediments are developed on the north flank of the mountains and, in part, are gravel-veneered.
150.1 U.S. Highway 180 rises through double road cuts in the Morrison Formation, which is veneered by gravel, on top of a pediment surface. To the north is an extensive area of Morrison exposures along the south bluffs of the San Juan River. Cross Tohache Wash.
152.4 The road descends through ledge and-slope topography carved on the Morrison Formation. Broad pediments are developed north of the Carrizo Mountains (fig. 2.18).
153.4 Cross Twin Falls Creek. Extensive exposures of green Morrison beds here show southeastward dip.
Figure 2.18. View southward from Mile 162 on the highway across Morrison beds to Cretaceous beds that are capped by volcanic rocks at the north end of the Carizzo Mountains. Broad pediments cut across the Morrison Formation and younger Cretaceous beds in close against the mountain front.
154.8 Cross-bedded channel sandstone in the Morrison Formation is exposed in double road cuts. Beyond the road cuts the highway drops to the floodplain of a small wash.
155.4 Teec Nos Pos Trading Post is approximately 1 mile south of the highway. U.S. Highway 180 in Morrison beds. Massive Morrison Sandstone is exposed along the canyon walls, particularly to the north. The volcanic crest of the Carrizo Mountains is well exposed beyond the pediment surfaces to the south (fig. 2.18).
156.0 Cross-bedded green and pinkish Morrison Sandstone in double road cuts. These beds are deposits from complexly braided streams.
164.4 Arizona State Highway Inspection Station.
156.6 Junction at Teec Nos Pas and Junction of Arizona State Highway 504 East to Shiprock with U.S. Highway 160. Turn north at the intersection. The Navajo Arts and Crafts Center is to the northeast of the intersection and a trading post is to the east, beyond the crafts center on Arizona State Highway 504. Turn north on U.S. Highway 160 toward Mesa Verde National Park, the Four Corners area, and Cortez and pass east of the Arizona State Highway Maintenance Station. U.S. Highway 160 continues between bluffs of light-colored sandstone and gray green shales of the Morrison Formation (fig. 2.19), whose slopes are strewn with boulders from the resistant sandstone on top and from a basalt flow which caps the ridges.
Figure 2.19. View to the south from Mile 158. Light-colored Morrison beds exposed near the bluffs are overlain by dark-weathering sandstone and basaltic debris. The Carrizo Mountains, beyond Teec Nos Pas, form the skyline in the distance.
158.0 The road descends northward from the Carrizo Mountains into the valley of the San Juan River. Ute Mountain laccolith is to the north, the La Plata Mountains to the northeast, the San Juan Basin toward the east and southeast, the Carrizo Mountains towards the south, and the Black Mesa Basin towards the southwest. Ridge crest is capped by brown-weathering sandstone of the Morrison Formation which is dipping northward from the Carrizo Mountain Uplift into the broad sag and the western end of the San Juan Basin.
162.2 Arizona-New Mexico State Line.
162.5 Junction Side Road West to the Four Corners Monument (fig. 2.20) (0.5 mile), the only point in the United States where four states meet. Continue northeastward towards Cortez through Morrison beds. From here the road begins to descend down to the valley of the San Juan River (fig. 2.21).
Figure 2.20. View northeastward across the Four Corners Junction, the only point in the United States where four states meet. Ute Mountain is on the skyline in the far distance.
Figure 2.21. Northward along U.S. Highway 160 to the crossing of the San Juan River. Light-colored exposures along the crest of the river bluffs, beyond the river, are Dakota Sandstone. The Ute Mountain laccolith forms the horizon.
164.2 Cross the San Juan River.
164.8 Terrace gravels of the San Juan River have been deposited over Morrison and Dakota beds. Braided stream-channel sandstones and beach sandstones are the prominent light-colored units in the Dakota Formation to the north.
165.5 Upper edge of terrace gravel. Shiprock is visible in the distance to the south, east of Carrizo Mountains. Terrace gravel still blankets the Cretaceous Dakota Formation and the basal Mancos Shale.
166.3 Coal-bearing beds of the Dakota Sandstone are exposed in the gully, with Dakota Sandstone forming the massive rim to the south (fig. 2.22). Terrace gravels here blanket the Mancos Shale along the north flank of San Juan Valley, beyond where the highway crosses the Dakota Formation (fig. 2.23).
Figure 2.22. Dakota Sandstone exposed in tributary gullys along the north side of the San Juan River, southeast of U.S. Highway 160 at approximately Mile 166.
167.0 Cross beneath the small bluff in Mancos Shale, protected by a thin calcareous sandstone unit. U.S. Highway 160 continues in the basal beds of the Mancos Shale.
168.0 oad cuts through light-colored calcareous sandy beds forming the prominent unit in the Mancos Shale.
Figure 2.23. Uppermost Dakota Sandstone and overlying thin coal beds at the base of the grey, slope-forming Mancos Shale, northeast of the highway at Mile 166.3. Ledges in the Mancos Shale are formed of calcareous sandstone or concretionary limestone layers. The entire sequence is overlain by coarse terrace gravels of the San Juan River.
171.6 Cross Aztec Creek. Bluffs of Man-cos Shale to the east are capped by terrace gravels of the San Juan River and are partly protected by a thin sandy zone (fig. 2.24).
172.5 The East and West Toes of the Sleeping Ute are visible as spires to the north, beyond the Mancos bluff.
173.5 Concretionary sandstone within the Mancos Shale forms the ledges on the bluff on either side and is the major protecting unit here along Aztec Creek.
Figure 2.24. Bluff in the lower part of the Mancos Shale, protected by concretionary thin sandstone units at Mile 172. The upper part of the bluff is also armoured by terrace gravels from the San Juan River, here along the Aztec Creek drainage.
174.6 The square-walled flat-bottomed meandering arroyo of Aztec Creek is typical of erosion features of alluvium on top of the Mancos Shale. The road climbs above the cuesta capped by the concretionary sandstone up into the middle part of the Mancos Shale and then continues eastward towards Mesa Verde in upper Mancos beds. Spires of Ute Mountain show well towards the north (fig. 2.25).
Figure 2.25. View north of the Ute Mountain laccolithic mass from approximately Mile 177. The Toes of the Sleeping Ute are the prominent spires of the southwestern margin. Mancos Shale forms the plains in the foreground.
177.3 Chimney Rock and Mesa Verde shows very well to the east. Mancos Creek has cut the notch directly to the east. Shiprock rises above the Mancos Platform to the south, east of the Carrizo Mountains.
180.2 The highway descends into tributaries of Mancos Creek. Mesa Verde rises to the east above the gray slopes of Mancos Shale, which are capped by the Point Lookout Sandstone. Above this the timbered, rounded crest of the mesa is held up by the coal-bearing Menefee Formation. Chimney Rock exposes basal beds of the Point Lookout Sandstone but not the uppermost beds.
181.2 Cross Navajo Springs Creek. A flat-bottomed, vertical-walled arroyo in alluvium and Mancos Shale.
182.4 Junction of U.S. Highway 160 with U.S. Highway 666. Both highways lead north towards Cortez. U.S. Highway 666 also leads south toward Shiprock. End of Guide Segment 2. For description of the geology along U.S. Highway 666 see HW-666 Road Guide..
from Field Guide: Northern Colorado Plateau by J. Keith Rigby - Purchase Information
