A dense population of endangered San Joaquin kit foxes occurs in the urban environment of Bakersfield, California.  Sarcoptic mange was detected in 2013 and rapidly spread causing a significant decline in kit fox abundance.  Kit foxes use dens on a daily basis.  Sarcoptic mange mites can live off-host under conditions found to occur in kit fox dens.  We monitored den use patterns of 37 kit foxes on the CSU-Bakersfield campus.  All foxes had unique dye marks and 20 were fitted with radio-collars.  During 390 one-week monitoring sessions, the proportion of sessions that other foxes used the same den as the collared fox within two, four, and seven days was 78.5%, 84.4 %, and 89.0%, respectively.  The mean number of other foxes using the dens was 1.8, 2.2, and 2.5, respectively.  Also, an average of 1.8 foxes was detected in a den concurrently with the collared fox during each week-long session.  During 120-day intervals (the time from infection to death), collared foxes used a mean of 7.6 dens, 9.8 other foxes used the same dens within one week, and 7.3 foxes used the dens concurrently with the collared foxes.  These results potentially explain the rapid spread of mange throughout this population.