Big Morongo Canyon Preserve, California, in Infrared The desert oasis at Big Morongo Canyon is one of the 10 largest cottonwood and willow riparian habitats in California.  The upstream end of the canyon lies in the Mojave Desert, while its downstream portion opens into the Colorado Desert. . The Preserve is managed by the Bureau of Land Management with the assistance of Friends of Big Morongo Canyon Preserve, a non-profit public charity.