The Tehachapis form a geographic, watershed, habitat, and rain shadow divide separating the San Joaquin Valley to the northwest and the Mojave Desert to the southeast.

The dramatic incline of Interstate 5 from the San Joaquin Valley floor up to the pass, is regionally referred to as The Grapevine, after Grapevine Canyon which it follows between the northern slopes of the two mountain ranges and is sometimes extended to include the portion of Interstate 5 on the southern side of Tejon Pass, especially during snow closures.

The Tehachapis are delineated from the Sierra Pelona Mountains by California State Route 138 at the range's southwestern end, connecting Interstate 5 and the Antelope Valley.

Their relative lack of development, especially in the large Tejon Ranch section, have allowed the continuity of these ecological functions to date.

[5] Montane species include: black oak (Quercus kelloggii), Coulter pine (Pinus coulteri), incense cedar (Calocedrus decurrens), white fir (Abies concolor), and in a few remote locations small stands of quaking aspen (Populus tremuloides).

There are at least 107 bird species, including the Steller's jay and mountain chickadee, found in the Tehachapis,[8] many which consume acorns of the black oak (Quercus kelloggii) as part of their diet.

They create a rain shadow for the eastern foothills ecotone into the Mojave climate zone that typically receives only a few inches of precipitation a year, usually in winter.

To the northwest lies the San Joaquin Valley with its grasslands and oak savanna climbing the broad western slopes of the range.

The Tehachapis collect marine and valley moisture, which piles up into fog that blankets the windward sides of the range many weeks of the year.

Canyons can have year-round surface water flow, even on southern slopes, from springs and orographic enhancements bringing extra precipitation and snow from passing storms.