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We estimated the total population size and sex and age ratios of mountain sheep, Ovis canadensis nelsoni, in the East Chocolate Mountains, Imperial County, California during 1992-1993. We collected data using ground observations, remote cameras, and helicopter surveys. Mark-recapture population estimates were based on 17 females and 8 males that had been fitted with radio collars. Of the three methods, only helicopter surveys met the assumptions inherent in mark-recapture sampling methodology. Based on helicopter surveys, we estimated that 160 animals inhabited the study area during 1993, with a 95% confidence interval of 138-203 individuals. The adult sex ratio was 74 males:100 females. Yearling ratios (13:100 females), fall lamb ratios (38:100 females) and high annual adult survivorship (0.95) suggest that the population increased during 1993.