The Trilobite Wilderness covers the Marble Mountains, a narrow volcanic range extending 12 miles in a northwest-southwest direction. Alternating dark brown and light brown striations have been tilted by geologic processes and give a marbled appearance to the range. Through the center, several yellowish sandstone peaks with long talus slopes are prominent. Trending eastward from the mountain range, the wilderness includes low rolling hills and sloping bajadas. Vegetation is characteristic of the lower Mojave Desert, consisting of creosote bush scrub and desert wash scrub. Wildlife is also typical for the Mojave Desert; including coyote, black-tailed jackrabbits, ground squirrels, kangaroo rats, quail, roadrunners, red tail hawks, prairie falcons, rattlesnakes, and several species of lizards. The area does have a very stable permanent population of bighorn sheep last estimated at around 150, and the eastern portion of the wilderness provides critical habitat for the threatened desert tortoise.