Terrace deposits along a 40 mile segment of the Colorado River between Austin and Bastrop, Texas, are mapped in detail. The following deposits have been delineated (lowest to highest): Floodplain, Sixth Street Terrace, Montopolis Terrace, Capitol Terrace, Hornsby Terrace, Asylum Terrace, and Delaney Terrace. The Hornsby Terrace deposits and the Montopolis Terrace deposits were previously unrecognized. A program of mechanical analysis was conducted on samples taken from the terrace deposits and the floodplain. Cumulative frequency curves of grain size from five samples collected up to 15 miles apart from the Asylum Terrace gravel, are distinctively grouped--different from all other samples. Cumulative frequency curves from five samples from the Hornsby Terrace gravel also plot in a close grouping distinct from other samples. Over short distances where abrasion is not a dominant factor it seems that grain size distribution may be useful as a means of correlation of terrace remnants. Analysis of the lithologies of these samples indicate that the Hornsby, Asylum and Delaney Terrace gravels are practically without limestone clasts, in a drainage basin that is, presently, composed dominantly of limestone. This suggests that the Commanche Series in the Edwards Plateau region was not extensively exposed but was covered by the Gulf Series at the time of the formation of these terraces. The Manor lag gravel, an upland gravel in the thesis area, is thought to be the remnant of a high terrace deposit of the Colorado River. All terrace gravels except the Capitol and Montopolis Terrace gravels are thought to be the result of lateral planation by a stream at or near grade. The Montopolis and Capitol Terrace gravels are thought to be the result of a lengthy episode of lateral planation by the Colorado River accompanied by slow degradation. / text

The Colorado River is the terrestrial part of a continental scale sediment routing system that has been evolving and carving the landscape of western North America for at least six million years. This study aims to test models of the geological evolution of the Colorado River in particular and the more general drainage history of the SW US. Several possible routes are proposed for the ancestral Colorado River prior to its integration across the Colorado Plateau and incision of the Grand Canyon. Palynological samples from prodelta deposits of the palaeo-Colorado River delta in the Salton Trough produced reworked pollen and dinoflagellate cysts from the river catchment. These provide strong evidence that the Colorado River was fully integrated across the Colorado Plateau during the early Pliocene, supporting heavy mineral data and U-Pb detrital zircon ages. Detrital zircon U-Pb dating provides accurate information for the source of sediment in the basins. Comparison with known ages of zircons in sedimentary units of the Colorado Plateau as well as local basement rocks in the basinal regions has identified two populations of zircons in the deltaic sediments: one from local Mesozoic plutonic basement and a second from Colorado Plateau stratigraphy. The data support recent work on the timing of integration of the river through the Grand Canyon, proving that the 5.33 Ma Colorado River that fed into the Salton Trough was integrated across the Colorado Plateau at that time and that there had already been a degree of incision of the Grand Canyon. A literature review shows how uplift of the Colorado Plateau and development of the San Andreas transform boundary had significant consequences for evolution of the Colorado River. The San Andreas Fault in southern California is responsible for the dextral lateral migration of the Los Angeles Basin and Salton Trough (both on the Pacific Plate) at least from Middle Eocene through Present. The Colorado River, which drains much of the western part of the North American Plate, crossed this major strike-slip plate boundary prior to deposition of the main part of its sedimentary load. The delta of the Colorado is in the v northern Gulf of California at the present day, but palaeo-reconstructions of lateral displacement along the fault show that the Salton Trough lay adjacent to the point where the Colorado River crossed from the North American Plate (at about 5.33 Ma). It is also possible that at about 18 Ma, at the time of fault initiation, the Los Angeles Basin was at the same point. The study uses heavy mineral analysis (HMA) and associated techniques to test the hypothesis that an ancestral Colorado River supplied sediment both to the Los Angeles Basin and the Salton Trough. Analysis of HMA data suggests a broadly similar source for some of the sediment in the two basins, and for the modern river. The data also indicate changes in the catchment area, suggesting that the Colorado River became fully integrated across the Colorado Plateau by the early Pliocene.

Thesis (M.S. - Hydrology and Water Resources)--University of Arizona, 1984. / Includes bibliographical references (leaves 46-47).

Thesis (M.S. - Hydrology and Water Resources Administration)--University of Arizona, 1985. / Includes bibliographical references (leaves 101-107).

Thesis (M.A. - History)--University of Arizona. / Includes bibliographical references (leaves 223-230).

Thesis (M. S. - Renewable Natural Resources)--University of Arizona, 2001. / Includes bibliographical references (leaves 155-156).

Thesis (M. S. - Renewable Natural Resources)--University of Arizona, 1998. / Includes bibliographical references (leaves 209-213).

Thesis (Ph. D. - Geosciences)--University of Arizona, 1987. / Includes bibliographical references (leaves 321-348).

Thesis (M.S.)--University of Wyoming, 2009. / Title from PDF title page (viewed on Jun 1, 2010). Includes bibliographical references (p. 107-116).

The Miocene to Pliocene southern Bouse Formation preserves a record of depositional environments immediately prior to and during integration of the Colorado River to the Gulf of California. Uncertainty over Bouse paleoenvironments obscures our understanding of the timing and magnitude of regional uplift, as well as the conditions and processes that were active during integration and early evolution of the Colorado River. Prior studies over the past 20 years have concluded that the southern Bouse Formation accumulated in chain of lakes isolated from the ocean. Sedimentologic analyses presented here aid interpretation of depositional environments and provide evidence for a strong tidal influence on deposition, consistent with a marine interpretation of other prior studies. This interpretation places a critical constrain on the elevation of these deposits at ca. 5 Ma, and suggests post-Miocene uplift of the Lower Colorado River corridor. This thesis includes previously published coauthored material.