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the interactions between the hydraulic energy of the flows, the bar sediments, and sediment delivery from upstream must produce a clast-supported, open framework conglomerate that forms the clean spawning substrate in which the constituent cobbles are at a condition of incipient motion. Initial validation of the PRM was done with data collected at RM 18.5 on the Yampa River at the Alternate Spawning Bar. Both the C1eopatras Couch and Alternate Spawning Bar sites were known squawfish spawning locations (Wick et aI., 1983; Tyus and MeAda, 1984; Tyus and Karp, 1989) and the physical characteristics of the sites were very similar (Harvey et aI., 1993). At the time of the data collection in 1991 at both sites the discharge was about 1,200 cfs. Fish capture data have indicated that there are other sites where the Colorado squawflsh may be spawning. These include Mathers Hole in the lower Yampa River (RM 17.5) and at the head of Gray Canyon on the Green River (- RM 155 upstream of Colorado River confluence). Wick (USDI, National Park Service, 1992, pars. comm.) reported that 15 adult squawfish (14 ripe and tuberculated males and 1 ripe female) were captured at Mathers Hole at a discharge of about 600 cfs in 1992. Tyus and Karp (1989), Tyus (1990) and unpublished U.S. Fish and Wildlife Service (USFWS) data (C. MeAda, written communication, 1993) indicate that there has been a long history of squawfish utilization of the Three Fords West spawning bar at the head of Gray Canyon (Tyus et at, 1982; Tyus et at, 1987). In 199222 Colorado squawflsh, 18 of which were ripe and tuberculated, were captured at this location (E. Wick pers. comm.). The physical characteristics of both the Mathers Hole and Three Fords West sites are different from the C1eopatras Couch and Alternate Spawning Bar sites. In the Fall of 1993, under very low flow conditions (- 300 cfs), field work was carried out at Mathers Hole and at C1eopatras Couch in the lower Yampa Canyon. A detailed topographic survey of Mathers Hole was conducted to characterize the topography of the bar and channel for use in subsequent one-dimensional hydraulic modeling (HEC-2). Fourteen cross sections were surveyed through the reach of interest and their endpoints were monumented for subsequent recovery. Wolman Counts (Wolman, 1954) of surface sediments were made at 11 locations and 6 bulk sediment samples were recovered from pits dug into the bar for subsequent laboratory analysis. Detailed geomorphic mapping of the bar and the reach in general was also carried out in the field. FIVe cross sections that had been previously established for IFIM data collection purposes were resurveyed at C1eopatras Couch to determine whether there had been significant changes following the relatively high peak flows during the 1993 runoff (17,600 cis). Wolman Counts were conducted at 6 locations at Cleopatras Couch as well. 1.4 Resource Consultants & Engineers, Inc.