Mormon Mountain is a dacite dome volcano that has given an age date of 3.1 million years. It's slopes are carpeted in a thick stand of Ponderosa pine trees, revealing that the eruptions are long dead here.
Written in Stone, the blog of my colleague Jack Share.
eolian sandstone, the cross-bedding evident dips to the south and east, documenting the dominant wind direction during the Permian Period some 275 million years ago. The Coconino attains its thickest section here along the Mogollon Rim and it thins northward beyond the Grand Canyon.
Here is a classic view of the Mogollon Rim just north of Payson and east of Highway 87. The lack of vegetation on the scarp is due to the Dude fire that scorched the trees in 1990. The rocks visible in the Mogollon Rim are Upper Paleozoic in age (about 285 to 270 million years old) and dip slightly to the north (left). This dip was imprinted in the rocks during the Laramide Orogeny when the Mogollon Highlands were raised in central Arizona (located far to the south or right in this photograph). As these Highlands were destroyed by Basin and Range faulting beginning about 17 million years ago, the Rim country became differentially elevated and the Rim emerged!
Approaching Payson, I look back to the north and see the lower Paleozoic section exposed at the base of the Rim. Seen in the cliff is the Tapeats Sandstone, most famous from exposures in the bottom of the Grand Canyon. The slope beneath the cliff is cut into the basement rocks.
The Great Unconformity is exposed in a road cut farther south. The bedded Tapeats Sandstone lies atop the basement rocks, here named the Payson Granite. More than 1,200 million years of earth history are missing at this contact.
The Tapeats Sandstone is a coarse-grained deposit interpreted to have been deposited along the shore of a Cambrian beach (525 million years ago). If you would like to see some of the trace fossils found in the Tapeats Sandstone from near the Payson area, see this blog here for descriptions and photographs.
My lecture was given to the Library Friends of Payson, a support group for the public library in town. They have an active group that meets monthly and use the Humanities Speakers Bureau for much of their meeting content.
"I think the health of our civilization, the depth of our awareness about the underpinnings of our culture, and our concern for the future, can all be tested by how well we support our libraries."
This is part of the reason why I enjoy giving these lectures about the geology of our state so much. These people are "salt of the earth" kind of folks, yet they rarely have an opportunity to learn about our science. When they are exposed to it, they not only enjoy it but can understand it and relate to it. We had a great time sharing with each other on this glorious fall day in Payson.