They extend for approximately 25 mi (40 km) southeast of the Santa Ana River east of the Elsinore Fault Zone to the Temecula Basin and form the western edge of the Perris Block.

The Temescal Mountains were originally considered to be bounded on the south by the San Jacinto River, by J. D. Whitney in his 1865 Geological Survey of California.

[6] Flora As part of the California Floristic Province, the Temescal Mountains host a diverse array of plant species within distinctive natural (plant) communities, including coastal sage scrub, chaparral, riparian woodland, southern oak woodland, rocky outcrop and valley grassland.

Fragrant sages, evergreen shrubs and trees, perennial bunchgrasses, Dudleya species of succulents, fire-following flowers and other wildflowers adorn the terrain.

Fauna Wildlife species found include mountain lion, mule deer, bobcat, coyote, raccoon, gray fox, American badger, spotted skunk, kangaroo rat, bats, ravens, red tailed hawk, mountain quail, canyon wren, speckled rattlesnake, Pacific rattlesnake, common kingsnake, gopher snake, two-striped garter snake, rosy boa, San Diego night snake, granite spiny lizard, arroyo toad, western spadefoot toad, various Aphonopelma species of tarantula, Quino checkerspot butterfly and many more.