Echinocactus polycephalus is a cactus that occurs in the Mojave Desert region of Arizona, California, and Nevada.

It also occurs in the Sonoran Desert region of southern California and northern Sonora, Mexico.

The plants grow in some of the most extreme arid environments in the American Southwest, such as Death Valley National Park, and the Mojave National Preserve of Southern California.

The stems of Echinocactus polycephalus are sometimes solitary, but more often in clusters of as many as 30, each up to 0.6 m tall.

The fruits are densely woolly, giving the common name cotton top cactus.