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New Evidence of Quaternary Faulting Along the Gore Range Frontal Fault, Summit County, Colorado

Description: 

The Gore Range Frontal fault (GRFF) is an east dipping, late Cenozoic normal fault that accommodates east-west extension associated with the northern Rio Grande Rift in central Colorado. The steep forested terrain along the eastern base of the Gore and Tenmile Ranges mask scarps within a complex geomorphic setting resulting from extensive landslides and multiple glaciations. Prior investigations have recognized sites with offset Quaternary deposits, principally along the northern section of the fault but have also shown that many of these sites are within or bounding large slope failures. USBR estimated a slip rate of 0.07 to 0.23 mm/yr on the northern part of the fault from scarp heights measured in glacial deposits and cosmogenic ¹⁰Be surface exposure dating of a single site along South Rock Creek from studies in 2010 and 2014. Prior mapping along the southern sections of the fault has generally shown the fault as queried or uncertain within areas of Quaternary cover.

In this study, we use the publicly available Summit County 1m lidar data collected in 2016 to systematically map evidence of offset Quaternary landforms and scarps along the GRFF at a scale of 1:10,000 between Hoosier Pass and Spruce Creek over a length of ~60-70 km. Our mapping shows a nearly continuous en echelon alignment of short (< 2 km), left-stepping scarps for the southern 60 km. This includes previously unmapped scarps in Late Quaternary moraines east of Quandary Peak and within the recessional moraines adjacent to the town of Frisco. The largest scarps are associated with the highest set of undated Mid (?) and Late Quaternary surfaces and moraines along the northern part of the fault. Smaller scarps are present in younger moraines, but scarps appear to be absent in the youngest late Pleistocene recessional moraines and across the modern (Holocene) valley floors.

Session: From Earthquakes to Plate Boundaries: Insights Into Fault Behavior Spanning Seconds to Millennia [Poster]

Type: Poster

Date: 4/20/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Mark S. Zellman

Student Presenter: No

Invited Presentation: 

Authors