The climate at Riverside is mediterranean with mild winters and occasional rains, Santa Ana winds from the desert, and rare early morning frosts. Summers are hot with occasional air inversion layers. Rainfall increases from 250 mm at Riverside to 1000 mm along the coastal slopes of the mountains, then decreases to 50 to 150 mm in the Mojave and Colorado deserts. Snow is common in the mountains above 2000 m, where ski resorts operate for several months. Mt. San Gorgonio (3,500 m) contains 10 late Pleistocene glacial cirques on its north slope which represent the southernmost glaciation in the United States. Strong environmental gradients produce remarkable vegetation diversity in the region. Chaparral and other brushland cover in the coastal valleys shift into majestic conifer forests on mountain summits, beyond which lay vast expanses of creosote bush scrub and alkali sink vegetation in the deserts.
Mountain and desert wildlands are mostly still in their pre-European pristine setting, and contrast with rapidly changing land use in the interior coastal valleys surrounding the campus. Riverside originally developed with citrus, notably the Washington Naval orange, which has been extensively planted on higher alluvial slopes to avoid winter freezes. Agriculture is now being replaced by small industry and rapid suburbanization. The city has a strong planning element of green belts, and protection of steeper hills and remaining citrus groves. Extensive plantings of palms, jacaranda, Peruvian peppers, eucalyptus, as well as other exotic or tropical trees lend a distinctive touch to a semi-tropical region.
UCR is located within a region undergoing rapid suburbanization. During the 1980s, the San Bernardino-Riverside Metropolitan Statistical Area was one of the fastest growing metropolitan areas in the nation in terms of population. Deserts, citrus groves, and dairy farms are undergoing conversion to urban land uses, such as regional malls, office parks, and tract residential subdivisions. Riverside attracts a large commuting population. The region is linked to Los Angeles's metropolitan rail network and is within one hour by car of major employment centers in Orange and Los Angeles Counties.
Local urban communities are actively engaged in local economic development and redevelopment programs. Urban growth is putting severe pressure on the habits of endangered species, such as the Stephen's Kangaroo Rat and the Fringe-Toed Lizard. Riverside County is establishing a system of reserves to protect local endangered species. Riverside provides a unique environment within which to study the interrelationships between urban growth and conservation planning.