Faculty Mentor

Chad Pritchard and Stacy Warren

Document Type

Poster

Publication Date

Spring 6-1-2021

Department

Geosciences

Abstract

The Palisades Park is a large City owned tract of land located on the western bluffs above Spokane. The purpose of this project was to create a geologic map and assess the features within the park for the benefit of a public conservation group, Friends of the Palisades. There are 3 main units identified by previous research in the vicinity. Volcanic rock units are part of the Columbia River Basalt Group (CRBG), which erupted primarily between 16.5 to 15.6 MA (Hammond 2013). Large sedimentary interbeds identified as Latah formation present between CRB flows (Swanson et al 1979a, 1979b). Latah formation is composed of composed of silts and clays, and can contain various plant fossils. The youngest units identified in the park are Quaternary Flood Deposits emplaced as a result of the cataclysmic Glacial Lake Missoula floods. The Missoula Floods occurred approximately 18000 years ago (O’Connor 2020 ), and were the most significant event in shaping the park. The flood deposits include poorly sorted sands and gravels, and accumulated anywhere where there was slack water. The project involved a detailed field mapping effort completed in April 2021. The park was surveyed on foot with each sample location marked using the mapping app StraboSpot to record data such as coordinates, geologic unit, etc. Basalt outcrops were sampled at select locations for XRF analysis at Eastern Washington University. Coordinates of sample locations were imported into ArcMap and draped over a DEM to determine a precise elevation. Results of XRF data were then correlated by elevation to create the geologic map for this study. This survey determined that Palisades Park contains the typical geology of the Columbia Plateau Flood Basalt province. In total, 3 separate members of the CRBG were identified; the Wapshilla Ridge and Sentinel Bluffs members of the Grande Ronde Formation, and the Priest Rapids member of the Wanapum Formation. Latah formation was observed in between flows, although exposure of the Latah is poor throughout the park. Megaflood features from the Missoula Floods including Potholes and flood gravel deposits were also observed in the park.

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