Research Article| February 01, 1979 Fossil ice-wedge polygons in the Colorado Front Range: Origin and significance J. B. BENEDICT J. B. BENEDICT 1Department of Anthropology, Colorado State University, Fort Collins, Colorado 80521 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1979) 90 (2): 173–180. https://doi.org/10.1130/0016-7606(1979)90<173:FIPITC>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation J. B. BENEDICT; Fossil ice-wedge polygons in the Colorado Front Range: Origin and significance. GSA Bulletin 1979;; 90 (2): 173–180. doi: https://doi.org/10.1130/0016-7606(1979)90<173:FIPITC>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Polygonal patterned ground in a tundra valley near Sawtooth Peak, Boulder County, Colorado, is unique in the Front Range because of its large size and its resemblance to fossil ice-wedge polygons. The polygons occur in a terminal moraine of latest Pinedale age (about 15,000 to 10,000 B.P.), at an altitude of 3,390 m. They range from 10 to 25 m in diameter and are outlined by shallow, vegetated troughs that show no surface indication of sorting. The polygonal ground pattern is attributed to thermal contraction cracking and ice-wedge formation during a late Pinedale or early Holocene cold interval in which permafrost existed at least 350 m below its present lower altitudinal limit. Frost-sorted rubble accumulated in troughs above the melting ice wedges; evidence of sorting, however, is concealed by humus-rich loessal or slope-wash sediments that bury the stones and fill interstices between them to form wedges of silty material as deep as 1.0 m. Organic matter in the humus-rich silt is believed to have eroded from an Altithermal A1 horizon during early Neoglaciation; radiocarbon dates of 5750 ± 110 and 5765 ± B.P. apply to formation of the Altithermal soil and are maximum ages for its erosion and redeposition, but they have no bearing on the time of patterned ground formation. Stones in the polygon borders have experienced no important frost sorting since the close of the Triple Lakes stade of Neoglaciation, which ended prior to 2855 ± 90 B.P. in the Sawtooth valley. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.