Rainbow Basin Natural Area
Map SatelliteThis area, fully protected, is one of the most important sites in the country for Miocene vertebrate fossils. They are found in the Barstow formation, a non-marine sedimentary with sandstone, fanglomerate, silt-stone and shale as well as minor amounts of fine volcanic debris. These sediments were deposited in lakes streams, and other wetlands that were occasionally subjected to volcanic dust and ash falls. Here, this formation is some 1,500 meters (5,000 feet) thick.
Among the numerous vertebrates discovered here are dog-bears, Hemicyonids, several horses, Hypohippus, Merychippus spp., and Archeophippus, pronghorns, Merycodus, peccaries, Byseohyus, several oreodonts, Brachycrus and Ustatochoerus, sabre-toothed cats, Machairodus, true cats, Pseudaelurus, mastodon, Gomphotherium (the first record in the State), camels, Hesperocamelus, as well as numerous other mammals and birds. Among the birds are fossil hawks, ducks, gulls and a quail-like bird, Cyrtonyx. There are also fossil tortoises and fresh-water molluscs. Fossil plants are sparse but palms were present.
Today the vegetation cover is creosote bush scrub. The rare plant, Psorothamnus arborescens, is found in the area.
Integrity: The area is protected as a State Park and Bureau of Land Management Natural Area. The remainder is private.
Use: Observational.
Ref: Merriam, J. C. 1919. Tertiary Mammalian Faunas of the Mohave Desert. Univ. of Calif. Dept. Geol. Sci. Bull. No.11, pp. 437-585.
March 1976
Inventory of California Natural Areas
Revision © 2009 Steven Louis Hartman