Crotalus oreganus helleri, commonly named the Southern Pacific Rattlesnake, is a venomous pit viper subspecies found in southwestern California and south into Baja California, Mexico.

The color pattern consists of a pale brown, gray-brown, or yellowish brown ground color overlaid with a series of large, dark brown dorsal blotches that may or may not have pale centers. The blotches are more diamond shaped, as opposed to those of C. o. oreganus that are more hexagonal, and are bordered by light scales. The tail rings are not clearly defined.

This snake is found in the United States in southern California, and in Mexico in northern Baja California, west of the desert. In the north it is found from the counties of San Luis Obispo and Kern, and south through the counties of Santa Barbara, Ventura, Los Angeles (including Santa Catalina Island and the foothills), southwestern San Bernardino, Orange, western Riverside, San Diego and extreme western Imperial. From there its range extends south through Baja California to lat. 28° 30' North.