| Sixtymile Formation | Kwagunt Formation | Galeros Formation | Nankoweap Formation |
| Cardenas Lava
| Dox Formation
| Shinumo Quartzite
| Hakatai Shale
| Bass Limestone |
The Dox Formation
The Dox Formation is a member of the Unkar Group and is by far the thickest of the Unkar Group formations. The only complete sequence of members in the Dox Formation occurs in eastern Grand Canyon where its overall thickness has been variously reported between about 3000 and 3200 feet. Its contact with the underlying Shinumo Quartzite is regarded to be generally conformable and marked by a relatively rapid subsidence and marine incursion. Geologists have divided the Dox Formation into four members: the lowermost Escalante Creek Member, Solomon Temple Member, Comanche Point Member and uppermost Ochoa Point Member. Their respective horizons are gradational and they are distinguished on the basis of color changes, topographic features and depositional environments.
Escalante Creek time was marked at its onset by relatively rapid subsidence of the area followed by gradual basin filling. By the close of Escalante Creek time the basin had filled and the region was at or near sea level, where it remained throughout the rest of Dox time. The overall lithologic sequence of the Dox members suggest the environment of deposition evolved from an underwater delta into a floodplain which was followed a tidal flat environment.
The Escalante Creek Member is reported to be 1280 feet thick where it is exposed in eastern Grand Canyon, where it consists of tan to greenish-brown siliceous quartz and calcareous arkose sandstones exceeding 800 feet in thickness overlaid with 400 feet of dark brown to green colored shales and mudstones. The overall tan to brown coloration of the Escalante Creek Member and its characteristic cliff-step topography differentiate it from the overlying Solomon Temple Member.
The Solomon Temple Member consists of cyclical sequences of reddish mudstones, siltstones and quartz sandstones that erode to form rounded, hilly structures that are characteristic for the overlying Comanche Point and Ochoa Point Members of the Dox as well. The overall thickness of the Solomon Temple Member is about 920 feet in eastern Grand Canyon. The lower 700 feet consist of a slope forming series of shaley siltstones and mudstones which are succeeded by 220 feet of maroon quartz sandstone. Channel features and low angle cross beds in the upper sandstones suggest a floodplain as their environment of deposition.
The Comanche Point Member is the most ubiquitously exposed member of the Dox in eastern Grand Canyon and occupies more than half the Dox outcrop area, where thicknesses for the Comanche Point Member ranging from 425 to 617 feet are reported. It is composed of sequences of shaley siltstones and mudstones with lesser occurrences of sandstone. White to pale green bands of leached redbeds up to 40 feet in thickness distributed about the Comanche Point Member provide its characteristic variegated appearance. Sedimentary structures in the Comanche Point Member include mud cracks, ripple marks, irregular, wavy bedding and salt casts. Stromatolitic dolomite layers occur in or on the horizons of the leached redbeds.
The uppermost member of the Dox Formation is its Ochoa Point member, which ranges in thickness from about 175 to 300 feet. It is composed of a cliff forming, micaceous mudstone that grades upward into a reddish, silty quartz sandstone. Sedimentary structures in the Ochoa Point member include salt casts in its mudstones, and ripple marks and cross beds in its sandstones, suggesting a tidal flat or shallow water marine for its environment of deposition.
The Ochoa and Comanche Point members were removed from the Dox sequence by subsequent erosion and are missing from the Dox in exposures west of Seventy-five Mile Creek.