The authors of Inventory of Amphibians and Reptiles at Hovenweep National Monument, 2001-2003 [https://irma.nps.gov/DataStore/DownloadFile/152888] observed only one rattlesnake during their survey. They classified it as Crotalus viridis concolor.

A more recent publication, the Safety section of the Hovenweep National Monument website [https://www.nps.gov/hove/planyourvisit/safety.htm] mentions the presense of "midget-faded rattlesnakes", Crotalus oreganus concolor, states that a visitor is "unlikely to see" them, and that they "generally flee when approached". None of the website claims proved true. We saw four of them, all very small, within a meter or less of the trail. They were not at all interested in moving away, all the while vigorously rattling their tails.