Rainbow Basin is a geological formation in the Calico Peaks range, located approximately 8 miles (13 km) north of Barstow in the Mojave Desert in San Bernardino County, California.

The basin is notable for the fantastic and beautiful[peacock prose] shapes of its rock formations as well as its fossil beds, which have provided scientists with valuable information about life during the middle Miocene epoch, between 12 and 16 million years ago; and to the northeast the Calico Early Man Site.

The lowest is called the Jackhammer Formation, and it is composed of layers of sandstone, siltstone, limestone, and conglomerate, all probably dating to the early Miocene Epoch (Dibblee 1968:18).

Finally, on top of everything else, is a relatively thin layer of fanglomerate (alluvial fan deposits) laid down during the late Pleistocene (Bureau of Land Management 1992:31).

Differential erosion of rocks of different hardness finished the job of sculpting the formations into the fantastic shapes that can be seen in Rainbow Basin today (Dibblee 1968:52).