The native vegetation of the San Ysidro Mountains represents the coastal sage scrub of the California coastal sage and chaparral ecoregion (western faces); and plants of the California montane chaparral and woodlands ecoregion (inland). The San Ysidro Mountains are one of the few locations the rare Tecate Cypress (Cupressus forbesii) is found. This tree was once abundant in the higher elevations of the range as well as in its canyons. The San Ysidro Mountains were deforested of living foliage by wildfires in 2003 and 2007. Cupressus forbesii is a fire ecology dependent species, and there has been some evidence of regrowth starting.