Presettlement ponderosa pine/Douglas-fir forests of the Colorado Front Range were open and heterogeneous. Logging, grazing, and fire suppression over past 100 to150 years have altered stand structure by changing diameter distributions and increasing overstory density. In an effort to guide forest restoration toward presettlement conditions, we are currently using the Forest Vegetation Simulator (FVS) to validate estimates of 1900 forest structure, and calibrate the model for future use, for an unmanaged landscape (unlogged, ungrazed, but fires suppressed since 1900). In 1997, tree data were collected in 15 0.1-ha plots at Cheesman Lake. For trees larger than 1.4 m tall, diameter at breast height, height, species, live/dead status, age, and diameter growth increment were recorded; for trees less than 1.4m tall, basal diameter, height, species, live/dead status, age, and height growth increment were measured. FVS was first calibrated with diameter and height growth increments from the plots so that it more adequately depicted our study area. A 1900 tree data file was derived from data collected in 1997 for each plot by including only the tree records that pre-dated 1900, and measuring 1900 d.b.h. on increment cores. The plot was then grown forward to 1997, with natural regeneration added each decade to represent ingrowth in the plot since 1900. The modeling results were compared to the actual data. Growth and mortality multipliers were modified and FVS was rerun until FVS-generated 1997 diameter distributions, stand densities, and canopy covers were similar to those observed in 1997. Results from this intermediate phase of research will help to guide restoration activities in the South Platte Watershed, Colorado, and will also be critical in future stages of our research.