The Boulder Mail Trail was used from 1902 to 1924 to deliver the mail by burros to Boulder, Utah. Boulder was one of the last settlements in the US to have automobile access. The route went over slick rock and canyons with a steep, precarious descent into a canyon known as Death Hollow, reputedly named as a result of the occasional loss of animals slipping to their death on the slick rock descent.
More historical information regarding one of the most spectacular backpacking treks in Utah can be found at
http://www.boulderutah.com/history.html or search for BOULDER MAIL TRAIL or DEATH HOLLOW, UTAH