Coyote Mountains
How and when they formed
The Coyote Mountains, located in a tectonically active region, have a complex history involving various rocks and immense natural forces. The foundation of the Coyote Mountains consists of ancient rocks formed during the Paleozoic and Jurassic eras. These rocks include types like marble, schist, and gneiss. They were initially buried deep beneath the Earth's surface but were lifted up and exposed due to seismic activity along the Elsinore Fault Zone.
As a result of this dynamic geological history, the Coyote Mountains offer a fascinating glimpse into the Earth's ancient past, with rocks and fossils telling the story of millions of years of geological activity.
22 to 14 million years ago
During the Miocene period, volcanic activity in the region resulted in the creation of various volcanic features like basalt flows and andesite plugs. These volcanic materials are mostly found on the eastern and southeastern parts of the mountains, particularly in an area known as the Painted Gorge, which showcases a colorful array of volcanic rocks.
6.3 to 4.3 million years ago
During the late Miocene, the Salton Trough region experienced a drop in elevation, leading to the intrusion of a shallow inland sea. This event deposited sedimentary rocks called the Imperial Formation directly over the older metamorphic and volcanic rocks. Fossils of corals and marine life are preserved in these rocks.
5 to 4.2 million years ago
The influence of the ancestral Gulf of California brought in sediments from the Colorado River delta, forming the Deguyños Formation during the early Pliocene. This marked the transition from a marine environment to a river delta.
4.2 to 2.8 million years ago
As time progressed in the Pliocene, the area saw further changes in sediment deposition. The marine delta turned into a meandering river system, resulting in the formation of the Arroyo Diablo Formation, characterized by sandstones and mudstones.
1 million years ago
Over time, more sediments, primarily the Hueso Formation, accumulated in the region until around 0.95 million years ago when tectonic activity and sediment accumulation ceased.
The geological evolution of the Coyote Mountains is closely tied to the movement of tectonic plates in the region. The area is part of the Salton Trough, a basin formed by the stretching and sinking of the Earth's crust. Major fault systems, such as the San Andreas Fault and the Elsinore Fault Zone, have played a significant role in shaping the landscape, causing the rapid uplift of rocks and exposing them to erosion by wind and rain.
Photo credits: John Fowler, Rick Bramhall