The geology of Fish Creek Wash, Split Mountain, and the surrounding area in Anza-Borrego Desert State Park is amazing and guaranteed to take you back a few million years.
Split Mountain Gorge, south of Ocotillo Wells, was created less than a million years ago as an antecedent stream cut down as the mountains slowly rose, creating a spit in what would have been a solid mountain range. The Vallecito Mountains are to the west and the Fish Creek Mountains are to the east.Diana Lindsay, “Anza-Borrego A to Z – People, Places and Things“, (Sunbelt Publications, 2001), 329
Split Mountain is one of the most heavily studied geological features in all of Southern California. The 3-mile-long canyon abruptly defines a unique, boulder-strewn layer cake of colorful fanglomerates, landslide deposits, gypsum beds, marine sediments (a good selection of marine invertebrates has been located near Split Mtn in Anza-Borrego Desert State Park), and abundant fossil “reefs” that punctuate the soft mudhills landscape of the Carrizo and Fish Creek badlands.Paul Remeika and Lowell Lindsay, “Geology of Anza-Borrego: Edge of Creation“, (Sierra Club Books, 2015), 120