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Raging floods uprooted thousands of hectares of forest vegetation in some years, but the flood-adapted riparian plants quickly reinvaded denuded areas. The river was dynamic, as was the vegetation that grew on its floodplain. There is some controversy concern- ing the original number, extent, and duration of backwaters along the lower Colorado River north of the border with Mexico. Ohmart et al. (1975) studied the dynamics of emergent wet- land formation along the river, reviewing historical records and eval- uating factors responsible for early marsh development. Early diaries (unpubl.) contain accounts of persons wandering for several days in wet areas that were choked with tules and other thick undergrowth, especially near Yuma. These accounts Initially create the impression that these marshes were quite extensive and per- sistent. However, study of the better-known and better-named backwaters In the historical record suggests that most backwaters were of small size, and their total lifespan was rarely more than 70 years and usually less (Ohmart et al. 1975). Another convincing perspective is offered by the noted biologist, Dr. Joseph Grinnell (1914), who led an expedition that floated the river from Needles to Yuma in 1910. Grinnell and his party, from the Museum of Vertebrate Zoology at the University of California-Berkeley, were on the river for three months collecting biological data. They compiled extensive field notes, col- lected plant and animal specimens, and studied the river as an ecological resource. Grinnell's party was on the river prior to the construction of any major dams (Laguna Dam was built in 1909 but silted in within six months). Of backwaters, Grinnell (1914:72-73) stated: The rivers habit of overflow would be expected to result in rather extensive tracts of palustrine flora. As a matter of fact, however, marshes were few and of small size. This was probably due to the rapid rate of evaporation of over- flow water so that favoring conditions did not last long, and also to the rapid silting- In of such water basins as ox- bow or cut-offs. As a result there were either almost life- less alkali depressions, or lagoons practically identical in biotic features with the main river. But in a few places there were well-defined palustrine tracts kept wet throughout the year, chiefly by seepage. They were marked by growths of tules, sedge [Carex spp. ], and salt-grass CDistichlis spp.], sometimes the latter alone, and were usually surrounded by the arrowweed or willow associa- tion. Prior to the construction of dams, the Colorado River was unpredictable in amount of flooding and Instream flow. This unpredictability con- tributed to the development of ephem- eral backwater wetlands. Grinnell (1914) gave the extremes of river flow as 113 to 2,832 m3/sec (4,000 to 100,000 ft3/sec), with the lowest flows occurring In midwinter and the highest in June. This high annual fluctuation in flow, combined with a constantly meandering channel and an arid desert climate, explained the short life expectancies of most back- waters. In addition, big floods car- ried heavy sediment loads that settled out as the floodwaters receded, ex- pediting the filling and drying of many marshes. Finally, seepage or subterranean water flow into the back- waters came primarily from washes that 20