Field trip no. 27 from “Geologic Excursions to the Rocky Mountains and Beyond,” field trip guidebook of the 1996 Annual Meeting of the Geological Society of America. (SP-44 has the complete set.) 13 pages. Digital PDF download. OF-96-04-27D
This field trip covers stops in Boulder and Jefferson Counties, beginning in the City of Boulder. Presented are examples of geologic contacts, landslide and rockfall hazards, soils types and ages.
Excerpted from the Introduction:
The Quaternary alluvial deposits form floodplains and flights of terraces, both along the mainstem of the South Platte River, and the numerous tributaries that flow out of the Front Range to eventually join the South Platte River. Madole (1991) reviews the dating of these deposits. The Holocene deposits (pre-Piney Creek, Piney Creek, and post-Piney Creek) have been radiocarbon dated, and the older ones dated either by U-series dating of bone (Szabo, 1980) or association with the Lava Creek ash of 0.64 ma. The Broadway Alluvium is considered to correlate with the Pinedale glaciation (ca. oxygen-isotope stage 2), and the Louviers Alluvium with the Bull Lake glaciation (ca. oxygen-isotope stage 6); two U-series dates on bone in Louviers Alluvium are 129 /- 10 ka and 86 /- 6 ka. A U-series date on a horn core in Slocum Alluvium is 190 /-50 ka. The Verdos Alluvium is dated by the included Lava Creek ash. Rocky Flats Alluvium is not dated, nor is the next older deposit, the Nussbaum Alluvium.