We describe population estimates, survival rates, and aspects of hibernation for a population of Zapus hudsonius preblei along a 3.7-km section of South Boulder Creek and 2 associated outflow ditches in Boulder County, Colorado. Mark-recapture analysis was used on 352 marked jumping mice with 722 captures from 6 paired sites along the creek and 2 sites on ditches. Linear population density estimates ranged from 22.7 ± 7.9 to 79.5 ± 33.3 animals/km of stream-reach for the 6 sites combined along South Boulder Creek, and from 33.9 ± 1.6 to 85.6 ± 30.3 animals/km along the occupied ditches. This study highlights the potential importance of irrigation ditches as suitable habitat for Z. h. preblei. Estimated over-winter survival rate for both sexes combined was 54.1 ± 18.8%, summer survival rate was 16.2 ± 9.6%, and combined annual survival rate was 8.8 ± 6.0%. We suggest that good hibernation habitat is important for these populations to offset low summer survival. First emergence from hibernation was 19 May 1999, the only year trapping was conducted during the emergence period. Males preceded females. Adults were captured in June with low post-hibernation weights and reached weights that would enable them to enter hibernation by the third week in August. Juveniles captured after mid September were considered to be offspring from second litters. By mid October in both years, no jumping mice were captured, and we infer that they had all entered hibernation.