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. be given to the fact that there are no streams in northwestern Colorado that have substantial flood evidence. Thus, the temporal flood record for Elkhead Creek Basin is extended regionally (spatially) by many observations of the non-occurrence of flooding (table 1). Because similar flood deposits have not been found in Elkhead Creek Basin, other northwest Colorado basins, or any other channel above 7,500 ft in Colorado, except for glacial outwash or dam-break floods (Jarrett and Costa, 1986; Jarrett, 1987, 1990b), no floods much greater than about bankfull in Elkhead Creek Basin (or any tributaries) have occurred during at least the last 8,000 to 10,000 years. The maximum paleoflood discharge in Elkhead Creek upstream from Elkhead Reservoir ranges from 1,600 to 3,360 ft3/S, The maximum paleoflood discharge in Elkhead Creek downstream from Elkhead Reservoir ranges from 4,500 to 4,750 ft3/s (table 1). Flood Depth and Paleostage Indicator (HWM-PSI) Relation . Onsite paleoflood investigations in northwestem Colorado utilized the elevation of the top of flood bars to estimate the minimum depth and discharge of past floods, The streams documented in the 1995 HWM- PSI comparison study cover the range of hydraulic and sedimentologic conditions of streams studied i Elkhead Creek Basin paleoflood study. The HWM-PSI data clearly demonstrates that the maximum elevation of the top of all new flood bars generally equals the 1995 HWM elevations (figures Sa and 8b). The 1995 and other available HWM-PSI data are summarized on figure 9 and indicate the top of the flood bars is with about +/-0.2 ft of HWMs for most sites, Exceptions are some streams having gradients larger than about 0.04 WfI where the top of the new flood bar protruded above the HWMs (figure 9), Thus, use of the elevation of the top of flood bars located in streams in northwestem Colorado streams provides a hydraulically reliable and accurate indication of the maximum depth and estimation of discharge for the paleofloods. Regional Analysis of Streamflow-Gaging Station Data There were 198 streamflow-gaging stations analyzed in northwestem Colorado, primarily in the Yampa and White River Basins; some have been operated since the early 19OOs. These gages are fairly unifonnly distributed by elevation. For these streamflow gages, maximum peak discharge is 33,200 ft3/s, unit discharge ranged from 1 to 477 ft3/sI mi2, drainage areas ranged from 0.08 to 7,660 mi2, gage elevation ranged from 5,235 to 10,500 ft, and there were a total of 3,512 station-years of record. To help define the maximum flood potential for northwestem Colorado flood data from ungaged sites that define maximum flooding from intense, localized rainstonns (Jarrett, 1987, 1990b; USGS flood data 1990-present) also were incorporated into the data base. For these additional data, the maximum peak discharge is 6,800 ft3/S, unit discharge ranged from 1 to 477 ft3/sI mi2, drainage area ranged from 1,1 to 629 mi2, and gage elevation ranged from 5,238 to 8,100 fl. . The maximum unit-discharge for each stream gage and ungaged streams is shown in figure lOa for northwestern Colorado. For the analysis of peak-flow data for streams above 5,235 fI in northwestern Colorado, the largest unit discharge is 477 ft3/slmi2 for Cottonwood Gulch near Rio Blanco (09306042), 21