DOI: 10.5066/p9312tdt
title: Extent of Pliocene hyaloclastic deposits and related lava flows in the Columbia Gorge, Oregon and Washington

description: This dataset contains polygons representing deposits of hyaloclastic debris that were generated between about 3.5 and 3.0 million years ago when a series of basaltic lava flows entered the canyon of the ancestral Columbia River. The lava flows were erupted from volcanoes in the area of the Hood River graben of McClaughry and others (2012), generally have low-potassium tholeiitic basalt composition, and were part of a widespread pulse of mafic volcanism in the northern Oregon Cascade Range that occurred between about 4.4 and 2.1 million years ago (Conrey and others, 1996). Lava flows that entered the ancestral Columbia River were rapidly chilled and fragmented during interaction with water (Trimble, 1963, Swanson, 1986; McClaughry and others, 2012). The voluminous hyaloclastic debris was swept downstream and accumulated as thick deposits in the eastern Portland Basin (Swanson, 1986). The canyon that the ancestral Columbia River occupied, known as the Bridal Veil channel (Tolan, 1982; Tolan and Beeson, 1984), was eventually filled by the hyaloclastite and related lava flows and the river was diverted to the north, where it has carved its present canyon. Argon?argon (40Ar/39Ar) age determinations for lava flows interbedded with and overlying the hyaloclastite (McClaughry and others, 2012; Fleck and others, 2014) suggest the hyaloclastite was deposited between about 3.5 and 3.0 million years ago. The hyaloclastic deposits (map unit Ttfh) are equivalent to the Troutdale Formation upper member of Tolan and Beeson (1984) and include the Troutdale Formation hyaloclastic sandstone member of Evarts (2006), Evarts and O'Connor (2008), Evarts, O'Connor, and Tolan (2013), and Wells and others (2020). Although the hyaloclastic deposits are generally sandstones in the western Columbia Gorge and Portland Basin, they contain pillow lavas and basaltic breccia in the area between Hood River, Oregon and Bonneville Dam. Most clasts in the hyaloclastic deposits are olivine-phyric basalt that is rich in basaltic glass (sideromelane) that is commonly altered to yellow-brown colored palagonite. At some localities in the western Columbia Gorge, the hyaloclastic deposits include beds of micaceous quartzose sandstone. This dataset also includes polygons representing the partial extents of lava flows (map unit Tlkt) that are either interbedded with or overlie the hyaloclastic deposits. The lava flows generally have tholeiitic basalt composition with low levels of potassium (less than 0.5 weight percent K2O), commonly contain olivine phenocrysts, and often have a diktytaxitic groundmass texture consisting of numerous small angular voids. The lava flows are equivalent to the late Pliocene lavas of the late High Cascades grouping of McClaughry and others (2012). It should be noted that there are numerous lava flows of similar age and composition in the region but this dataset mostly contains those that can be used to constrain the history of the hyaloclastic deposits in the Bridal Veil channel. This data release is a compilation that includes incomplete geologic mapping and it is anticipated that extents of these deposits will be expanded in future geologic maps. The source maps upon which most of this dataset was derived from were intended for use at 1:24,000 scale. References Cited: Conrey, R.M., Sherrod, D.R., Uto, K., and Uchiumi, S., 1996, Potassium-argon ages from Mount Hood area of Cascade Range, northern Oregon: Isochron/West, no. 63, p. 10-20. Evarts, R.C., 2006, Geologic map of the Lacamas Creek quadrangle, Clark County, Washington, U.S. Geological Survey Scientific Investigations Map 2924, scale 1:24,000, https://doi.org/10.3133/sim2924. Evarts, R.C., and O'Connor, J.E., 2008, Geologic map of the Camas Quadrangle, Clark County, Washington, and Multnomah County, Oregon, U.S. Geological Survey Scientific Investigations Map 3017, scale 1:24,000, https://doi.org/10.3133/sim3017. Evarts, R.C., O'Connor, J.E., and Tolan, T.L., 2013, Geologic map of the Washougal quadrangle, Clark County, Washington, and Multnomah County, Oregon, U. S. Geological Survey Scientific Investigations Map 3257, scale 1:24,000, https://doi.org/10.3133/sim3257. Fleck, R.J., Hagstrum, J.T., Calvert, A.T., Evarts, R.C., and Conrey, R.M., 2014, 40Ar/39Ar geochronology, paleomagnetism, and evolution of the Boring volcanic field, Oregon and Washington, USA: Geosphere, v. 10, no. 6, p. 1283-1314, https://doi.org/10.1130/ges00985.1. McClaughry, J.D., Wiley, T.J., Conrey, R.M., Jones, C.B., and Lite, K.E., 2012, Digital geologic map of the Hood River Valley, Hood River and Wasco Counties, Oregon: Open-File Report O-12-03, 130 p., https://www.oregongeology.org/pubs/ofr/p-O-12-03.htm. Swanson, R.D., 1986, A stratigraphic-geochemical study of the Troutdale Formation and Sandy River Mudstone in the Portland basin and lower Columbia River Gorge, Portland State University, M.S. thesis, 115 p, https://doi.org/10.15760/etd.5604. Tolan, T.L., 1982, The stratigraphic relationships of the Columbia River Basalt Group in the lower Columbia River Gorge of Oregon and Washington, Portland State University, M.S. thesis, 169 p, https://doi.org/10.15760/etd.3232. Tolan, T.L., and Beeson, M.H., 1984, Intracanyon flows of the Columbia River Basalt Group in the lower Columbia River Gorge and their relationship to the Troutdale Formation: GSA Bulletin, v. 95, no. 4, p. 463-477, https://doi.org/10.1130/0016-7606(1984)95%3C463:IFOTCR%3E2.0.CO;2. Trimble, D.E., 1963, Geology of Portland, Oregon, and adjacent areas: U. S. Geological Survey Bulletin 1119, https://doi.org/10.3133/b1119. Wells, R.E., Haugerud, R.A., Niem, A.R., Niem, W.A., Ma, L., Evarts, R.C., O'Connor, J.E., Madin, I.P., Sherrod, D.R., Beeson, M.H., Tolan, T.L., Wheeler, K.L., Hanson, W.B., and Sawlan, M.G., 2020, Geologic map of the greater Portland metropolitan area and surrounding region, Oregon and Washington: U.S. Geological Survey Scientific Investigations Map 3443, scale 1:63,360, https://doi.org/10.3133/sim3443.