This snake can be found in the southwestern parts of the United States, Mexico, south to Oaxaca. In the US, you can find it in Arizona, central and west Texas, the Gulf of California, Tiburón Islands, and San Estéban.
This species is terrestrial and can be found on grasslands, deserts, and rocky areas. Even though they are terrestrial, they are able swimmers and climbers. They are diurnal in spring and fall but become nocturnal in the heat of summer, but in winter they hibernate in borrowed dens. They feed primarily on rodents, small mammals, small reptiles and birds. Females give birth to live young ones in the summer. The young hatch and are cared for by their mothers in less than two days. The litters can be as many as ten or twelve.
This is a venomous, medium-sized species of snake that averages a length range of 30-40 in, with a maximum length of about 50 inches in rare cases. Females are usually larger than males. The colors range from yellow and olive green to brown and black and as the name implies, their tails are completely composed of black scales. Most specimens have a black band across the eye that runs diagonally and ends at the corners of the mouth, this gives them the appearance of a mask. This rattlesnake has a keratin rattle at the end of its tail. The rattle itself is a bit fragile and is susceptible to breakage.
Learn more with Schechter Natural History's Guide to Reptiles and Amphibians