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. made to help place extreme floods in perspective with present understanding of flood hydrology (National Research Council, 1985; Jarrett and Costa, 1988). The recurrence interval for the maximum paleofloods on Elkhead Creek ranges from about 1,000 to 10,000 years. The 1 O,OOO-yr flood estimate for Elkhead Creek is about 6,500 fl3/s at Elkhead Dam. The PMF at Elkhead Dam (Ayres Associates, written commun., 1996) is 36,052 ft3/S. Using the flood-frequency relations developed in this study, the PMF has a recurrence interval in excess of a million years. The maximum paleoflood of 4,750 fl3/s in at least 1 0,000 years in Elkhead Creek is about 13 percent of the PMF. Similar difference in maximum flood potential have been documented for other Rocky Mountain streams where paleoflood studies have been conducted. Flood potential in northwestem Colorado appears to be smaller than anywhere else in Colorado, except perhaps streams in North and South Parks, These study results complement and extend the documentation of elevation limits to substantial rainfall-produced flooding throughout the Rocky Mountains. Many intermittent streams in northwestem Colorado have very little evidence of substantial runoff. A lack of channel development is due to: (1) little snowpack and snowmelt runoff; and (2) these tributaries are above the elevation for substantial rainfall intensities, amounts, and have a limited areal extent of rainstorms and thus rainfall runoff, An assessment was made of the likelihood that the PMF would not have occurred by chance in the study area. The probability that the PMF would not have occurred in Elkhead Creek Basin in 10,000 . years is 1.183 xl~, and the probability that the PMF would not have occurred in and part of northwestem Colorado in 10,000 years is 3.3xl 0'37. Conversely, the probability that the PMF is expected to have occurred is 0.9817 in the Elkhead Creek Basin and essentially is 1 for the PMF to occur in at least one basin within the 4,200 mi2 study area. These probabilities help demonstrate that paleoflood evidence for the PMF-based floods should have been identified if not in Elkhead Creek Basin, then certainly in at least one basin in northwestem Colorado, Thus, it raises further question as to the magnitude of the PMF estimate for Elkhead Creek, Large differences between the PMP/PMF-based hydrology and paleoflood estimates for Elkhead Creek and similar comparisons for numerous other rivers in Colorado and the westem United States indicate the need to improve the understanding of flood hydrometeorology and reduce the uncertainty of extreme rainfall and flood estimates. The most likely explanation for excessive PMP/PMF estimates in the Rocky Mountains are: (1) transposition of distant low elevation storms; (2) precipitation maximization that does not account for observed decreases in extreme, short duration precipitation with increasing elevation; (3) remoteness from moisture sources; (4) use of questionable extreme rainfall and flood data to make flood estimates; and (5) overestimation of the areal extent of extreme rainstorms. Although both the PMP/PMF method and paleoflood techniques have uncertainties, maximum- paleoflood estimates are based on physical evidence of extreme floods that are preserved in and along . channels. Regional, interdisciplinary meteorologic, hydrologic, and paleoflood investigations provide valuable information for integrating the complex response and uncertainties of a river basin to extreme 34