Geographic range: Nearctic, Neotropical: USA and Mexico. From Texas to Sonora, Chihuahua, Nuevo León, Coahuila, Durango, Tamaulipas, Sonora, San Luis Potosí, Zacatecas, Aguascalientes, Guanajuato, Querétaro, México, Distrito Federal, Puebla, Veracruz and Oaxaca

Physical characteristics: This is a medium sized rattlesnake that reaches a length of 120 cm. The general ground color maybe brownish olive, yellowish olive or brownish gray, posteriorly the ground color becomes more darkly suffused with brownish black to black pigment, which extends onto the tail., in most snakes the pattern on the posterior one third is complety obscured by dark pigmentation, 24-34 dark brown or black rhomboidal or diamond shaped blotches are bordered by yellow or yellowish gray scales and the pale borders, the head is black, a dark postocular stripe is clearly evident.

Food habits: Feeds mostly mammals, principally in rodents populations.

Reproduction: This snake is viviparous, the mating are observed in early spring and the young are born in the early summer. The litter size is 5 to 16.

Behavior: Most snakes have been observed basking in the late morning during the July -August rainy season, it can have crepuscular activity but never at night.

Habitat: It is found in pine-oak forest, pine-fir forest, oak-grass savanna, boreal forest, mesquite grassland, desert scrub and probably thorn forest. This species occurs frequently in rocky areas or in lava beds areas.

text: © Alfonso Delgadillo