PERMFILE40846 - Laserfiche WebLink

Home Browse Search

I 9 • ~I review and cites nearly 100 pertinent references dealing with the topic. He ? provides details of the multiple erosion surfaces, peneplains and pedi- ll plains dating back to Tertiary. This discussion will focus only on quater- nary aspects of landforni development along the Purgatoire River. 1 The Purgatoire River heads in the Sangre de Cristo Range south of the Spanish Peaks and flows eastward into the Raton Basin eventually joining the Arkansas River. The Purgatoire is a consequent stream whose location is not controlled by lithologic nor structural anisotropies. The head- y waters of the Purgatoire are underlain by volcanic rocks and Pleistocene 1 glacial-fluvial sediments. In its downstream course the river flows across )( the foothills belt of Paleozoic-Mesozoic strata, the terrestrial sediments J of Tertiary age including the study area and thence across the marine Pierre 11 Shale. lithologic control of the geomorphology and channel geometry can be detected in the various terrains and changing water quality shouid like- ~~ wise be expected. Clearly, a natural deterioration of water quality can be expected in streams flowing out of igneous terrains and onto marine sediments such as the Pierre Shale. • 1~ The high level erosion surfaces that have been previously studied in ~~ the region are not represented in the study area. They are situated mare than a thousand feet above Purgatoire, are represented by alluvial deposits above and below lava flaws and are thought to be mid to late Tertiary in ages I! Three levels of pediments have been named in the region (Levings, 1951}. They are truncated, gravel-capped surfaces that are slightly concave upward jl rn longitudinal profile and are best represented on the plains east of the study area. fie surfaces have 6eert cut on relatively weak sedimentary rock .I and the gravels are composed bf igneous and metamorphic clasts probably derived from the high level surfaces and the Raton formation. It is doubtful that current workers would use the term pediment for these surfaces as they j tend to be concordant to bedding and structure. I~ The study area contains two levels of rock benches that formerly may have been referred to as Beshoar and Barilla pediments. We inter rp 2t these • ~ as strath terraces with an alluviat_veneer. Both features are shown on I~ Plate-2"with o__nly the lower on Plate 3 (plates are contained in pocket on rear cover).