The eastern is the heaviest venomous snake in the Americas and the largest rattlesnake. It is found in the southeastern US. The western is found in the western US and northern Mexico, and is believed to be the cause of most of the snakebite fatalities in northern Mexico and is second for same in the US. Eastern: http://en.wikipedia.org/wiki/Crotalus_adamanteus Western: http://en.wikipedia.org/wiki/Crotalus_atrox Eastern: The color pattern consists of a brownish, brownish yellow, brownish gray or olive ground color, overlaid with a series of 24-35 dark brown to black diamonds with slightly lighter centres. Each of these diamond-shaped blotches is outlined with a row of cream or yellowish scales. Posteriorly the diamond shapes become more like cross-bands and are followed by 5-10 bands around the tail. The belly is a yellowish or cream color with diffused dark mottling along the sides. The head has a dark postocular stripe that extends from behind the eye backwards and downwards to the lip; the back of the stripe touches the angle of the mouth. Anteriorly and posteriorly, the postocular stripe is bordered by distinct white or yellow stripes. Western: The color pattern generally consists of a dusty looking gray-brown ground color, but it may also be pinkish brown, brick red, yellowish, pinkish or chalky white. This ground color is overlaid dorsally with a series of 24-25 dorsal body blotches that are dark gray-brown to brown in color. The first of these may be a pair of short stripes that extend backwards to eventually merge. Some of the first few blotches may be somewhat rectangular, but then become more hexagonal and eventually take on a distinctive diamond shape. The tail has 2-8 (usually 4-6) black bands separated by interspaces that are ash white or pale gray; this led to the nickname of "coon tail." There is a postocular stripe that is smoky gray or dark gray-brown and extends diagonally from the lower edge of the eye across the side of the head. This stripe is usually bordered below by a white stripe running from the upper preocular down to the supralabials just below and behind the eye.[5] Its off-white belly is usually unmarked, its anal scale is undivided, and its dorsal scales are extremely keeled, often in rows of 25 to 27 near midbody.