I most often find these huge toads lumbering around looking for mates or food. Female. Despite the trip’s short duration, the effects of toad venom — which is extracted from Colorado River toads, also known as Sonoran Desert toads — come on strongly and immediately. The California toad has a distinct light dorsal stripe while the Yosemite Toad has a faint light stripe or no stripe. The Sonoran Desert toad (Bufo alvarius) weighs in at little more than 2 pounds and is 8 inches long. I can imagine that to other frogs and toads in and around the ponds Bufo alvarius (aka the Colorado River toad) must look like a T-rex. They do not occur with any other species of toad, although the California Toad occurs nearby. Yosemite toads only occur at high elevations in the Sierra Nevada Mountains. It is the largest toad native to the United States.