 Although 17 subspecies are recognized , this number may be excessive . Using a cluster analysis of anatomical characters , Dixon and others found that black @-@ tailed jackrabbit subspecies separated into two distinct groups that are geographically separated west and east of the Colorado Rocky Mountains and the Colorado River . They suggested only two <unk> are warranted : the western subspecies L. c. californicus and the eastern subspecies L. c. <unk> . 
