MONITOR BUTTE MEMBER
Composed of greenish claystones, mudstones, sandstones and conglomerates, this unit ranges from 50 feet thick near Holbrook to 350 feet thick in the Defiance Plateau. It is also found in abundance at the Zuni Mountains and Monument Valley. It weathers into thin irregular ledges and commonly caps buttes in the area. Grayish red sandstone ledges are characteristic of this unit. In St. Johns in the Blue Hills area, the green claystones yield many fossil teeth and bones of Metoposaurs and Phytosaurs. Also, coarse sandstones in the area contain huge neocalimites, and patterns of insect burrows.
Pastel colored bentonite clays eroding for form banded badlands unique to the Chinle. This shot was taken within the Blue Hills at St. Johns with the land owners permission during a paleontological survey of this member by the Southwest Paleontological Society in Mesa, Az. Certain beds within the multi banded hills contained the remains of large reptiles, including teeth, bones and scutes. Other beds contained the classic green clays of the Monitor Butte member and within them, one could find additional types of fossils including white coprolites fish and reptiles.
Another view from the Blue Hills in St. Johns. In the valleys between the ridges, one could often find a concentration of silicified material, including permineralized wood, more reptile teeth and scutes, and fossil roots and stumps. We also found preserved sedimentary structures such as wave ripples, tooling marks, and trace fossils.
My wife Dawn stands on a ridge in St. Johns, during our museum sponsored survey. The most stark landscapes are found in these badlands, where the expansion of the clays forming the hills do not allow any plant growth at all.
Fossil beetle burrows - found in the brown siltstone facies at St. Johns. They were about 1/4 to 3/8 inch in diameter, up to an inch deep, and rounded on the bottom. The sides of the burrows were also "rifled" with spiral grooves on the interior. These have been interpreted by some workers as escape structures for the hatching of larvae.