THE DISCOVERY AND DISTRIBUTION OF MAMMOTH REMAINS IN BENTON COUNTY, WASHINGTON STATE

Located in the heart of the Columbia Basin geographic province, Benton County occupies an important piece of Ice Age geography in the Pacific Northwest. During the late Pleistocene geologic constriction at Wallula Gap impounded dozens of catastrophic Missoula Floods forming multiple ephemeral versions of Lake Lewis. Fine-grained sediments from these temporary lakes, collectively known as the Touchet Beds, cover much of Benton County up to 330 m above sea level. Loess (wind deposited sediments) blanket these flood deposits throughout much of the county. Mammoth (Mammuthus spp.) subfossils are common finds in the Touchet Beds (most recently at the Coyote Canyon Mammoth Site, southwest of Kennewick); many are also reported in late Pleistocene loess deposits in the county. Benton County may be divided into three geographic subprovinces: Horse Heaven Hills, Pasco Basin, and lower Yakima River Valley. All three subprovinces of Benton County have produced mammoth finds, although not in equal numbers. Here we present data gathered from newspaper accounts, museum collections, published reports, and personal accounts that document the remains of at least 45 mammoths from Benton County, with an additional 10 proboscidean finds (tusks, non-diagnostic bones) that may also plausibly be interpreted as being from mammoths as well. Thirty (66.3%) of the mammoth finds from the county are from the Horse Heaven Hills subprovince, reflecting extensive surface surveying by paleontologists and archaeologists in the 1960s. Foremost among these was a series of paleontology surveys conducted by Fry (1969) over some 25 square miles of this subprovince. Fry’s research documented 21 mammoth finds, and represents 70% of the finds currently known from the Horse Heaven Hills. Eleven mammoths have been reported from the Pasco Basin, accounting for roughly 24.3% of the mammoths known from Benton County. Most of these finds stem from private/commercial/state-federal construction projects that have deeply and extensively sampled the late Pleistocene sediments of this subprovince. Four (9.3%) of the county’s mammoth finds have been reported from the lower Yakima River Valley. Many of these were found during agricultural and construction activities related to population growth. These distributional disparities merit further investigation.