The animal is considered threatened in New Mexico, with its numbers in decline in recent years; its presence is uncertain in Arizona.

A median black line concealed by sooty, brownish, and white-tipped hairs divides the rump.

The head is a cream buff color, mixed with black, with whitish areas around the sides of the eyes.

The ears are covered with short yellowish-brown hairs that are mixed with black anteriorly and white posteriorly.

The winter pelage of the white-sided jackrabbit is iron gray on the rump, back, and outside of the hind legs.

The underside of the neck is dark grayish bluff and the remaining underparts, including the flanks, are white.

The young tend to have a soft, woolly coat in early life and attain sexual maturity at a rapid rate.

When startled by or alarmed by a predator, it leaps straight upwards while extending the hind legs and flashing the white sides.

The long hind legs and feet are adapted for speed, giving the animal lift and an ability to run in a zig-zag fashion that surpasses its pursuers.

The long ears serve to locate sound, as well as regulate temperature when they are raised like a fan to catch passing breezes in hot conditions.

The eyes, like those of most nocturnal or crepuscular animals, are laterally arranged, giving them a complete field of vision (360°).

The food is ingested by chewing the grass sticking out of the mouth, with the head raised and the body sitting in a crouched position.

When eating certain nutgrass, however, the fore paws are used to excavate the bulbous tubers, leaving behind oval foraging depressions in which fecal pellets are often deposited.

A third vocalization, consisting of a trilling grunt, is heard during the sexual chase of the white-sided jackrabbit, but it is not known which member of the pair makes this sound.

The diet of the white-sided jackrabbit consists primarily of grasses including buffalograss, tobosagrass, fiddleneck, wolftail, blue grama, vine mesquite, ring muhly, wooly Indian wheat, and Wright buckwheat.

As a result, the overgrazing of domestic livestock may be one of the factors contributing to its decline and the apparent replacement by the black-tailed jackrabbit (Lepus californicus), which has been highly adaptable to these habitat changes.