Lack of Euro-American disturbance, except fire suppression, has preserved the patterns of forest structure that resulted from the presettlement disturbance regime in a ponderosa pine/Douglas-fir landscape at Cheesman Lake in the Colorado Front Range. A mixed-severity fire regime and variable timing of tree recruitment created a heterogeneous forest age structure with considerable old growth. Surrounding forests subjected to human alteration since the late 1800s are younger, denser, and more continuous. We present preliminary data from a study of fire history and age structure. We mapped forest patches based on tree size and density using color-infrared aerial photos, then randomly sampled 10 percent of these patches across the 35 km2 landscape for the ages of the five apparent oldest trees. Trees older than 200 years were found in 70 percent of sampled stands. Trees older than 400 years were found in 30 percent of sampled stands, suggesting that old growth was common and widespread in historical landscapes in the Front Range. We compared the stand ages with locations of known fire dates derived from fire scars. Concentrations of trees that postdate known fires indicate a past stand-replacing fire. Such postfire cohorts are discernible as far back as 1531 A.D. Of 21 fires recorded by scars between 1531 and 1880, 16 appear to have had a stand-replacing component, and seven known fires predate 71 percent of the postfire cohorts. Time between stand-replacing disturbance and tree establishment varied considerably between sites, but generally ranged from 20 to 50 years. Some openings began to regenerate within 10 years after fire, while others remain unforested 150 years later.