Ringold Formation

Ringold Formation
Name	Ringold Formation
Type	Geological formation
Age	Miocene to Pliocene
Period	Neogene
Prilithology	Fluvial sandstone, siltstone, conglomerate
Otherlithology	Lacustrine deposits
Namedfor	Ringold, Washington
Namedby	Mackin (1961)
Region	Columbia Plateau, Washington
Country	United States
Overlies	Columbia River Basalt Group
Underlies	Pasco Basin sediments, Quaternary deposits
Thickness	Up to 300 meters
Extent	Benton, Franklin, and Walla Walla Counties

Ringold Formation. The Ringold Formation is a significant Neogene sedimentary sequence exposed within the Pasco Basin of the Columbia Plateau in Washington. It unconformably overlies the extensive Columbia River Basalt Group and preserves a detailed record of fluvial and lacustrine environments following the main phase of flood basalt volcanism. Studied extensively since its definition by J. Hoover Mackin in 1961, the formation provides critical insights into the region's paleogeography, paleontology, and hydrogeology.

Overview and Description

The Ringold Formation consists primarily of poorly to moderately consolidated fluvial deposits, including cross-bedded sandstone, siltstone, and channel-fill conglomerate, interbedded with fine-grained lacustrine sediments. These strata are prominently exposed along the walls of the Columbia River and its tributaries, such as the Snake River and Yakima River. The unit is named for exposures near the town of Ringold, Washington, within Benton County. Its distinctive lithology and fossil content differentiate it sharply from the underlying Columbia River Basalt Group and the overlying Quaternary loess and Missoula Floods deposits. The formation's variable thickness, reaching up to 300 meters, reflects the complex topography of the eroded basalt surface upon which it was deposited.

Stratigraphy and Age

Stratigraphically, the Ringold Formation rests unconformably on the top of the Columbia River Basalt Group, specifically on units like the Saddle Mountains Basalt. It is overlain disconformably by younger Pleistocene sediments associated with the Pasco Basin and catastrophic Missoula Floods. The age of the formation is constrained by magnetostratigraphy, fission track dating, and biostratigraphy of contained fossils. These methods date the bulk of the deposition from the late Miocene through the Pliocene, approximately 8 to 3 million years ago. The unit is often subdivided into informal lower and upper members based on lithological shifts, with the upper sections typically finer-grained, indicating a transition in depositional energy.

Depositional Environment

The sedimentary structures and facies of the Ringold Formation indicate deposition within a long-lived, low-gradient fluvial system that drained the evolving Columbia Basin. This system included broad, meandering river channels, extensive floodplains, and occasional large lakes, potentially influenced by tectonic subsidence in the Pasco Basin. The presence of lacustrine deposits, including diatomaceous siltstones, suggests periods of ponding, possibly due to landslide dams or volcanic barriers within the ancestral Columbia River drainage. The overall environment is interpreted as a semi-arid to temperate floodplain, supporting riparian forests and open woodlands, distinct from the volcanic deserts that preceded it and the glacial climates that followed.

Paleontology and Fossils

The Ringold Formation is renowned for its diverse fossil assemblage, which provides a snapshot of Miocene-Pliocene life in the Pacific Northwest. Vertebrate fossils are abundant and include remains of the gomphothere *Gomphotherium*, the rhinoceros *Teleoceras*, the camel *Megatylopus*, and various equids like *Hipparion*. These finds are complemented by fossils of turtles, fish such as salmon, and small mammals. The flora is represented by petrified wood, leaf impressions, and pollen records, indicating forests dominated by bald cypress, oak, and elm. This biota collectively points to a warmer, more mesic climate than present, with significant riparian corridors.

Economic Significance

Economically, the Ringold Formation is a critical hydrogeologic unit within the Columbia Plateau aquifer system. Its porous sandstones and conglomerates form important regional aquifers, supplying water for agriculture, municipalities, and the Hanford Site. The formation's sediments also host commercially valuable deposits of sand and gravel for construction. Furthermore, the fossil-rich layers are of significant interest for paleontological research and education, with specimens housed in institutions like the Burke Museum of Natural History and Culture and the Thomas C. Savage Memorial Museum.

Geological Context and Correlation

The Ringold Formation records the sedimentary response to the cessation of major flood basalt volcanism from the Columbia River Basalt Group. It correlates temporally and environmentally with other late Neogene basin-fill deposits across the Intermontane West, such as the Thousand Creek Formation in Nevada and parts of the Idaho Group. Its deposition coincides with major orogenic events in the Cascade Range and continued uplift of the Rocky Mountains, which influenced regional drainage patterns. The formation's top is sharply truncated by Pleistocene glaciation and the subsequent cataclysmic Missoula Floods, which scoured the Channeled Scablands and deposited the overlying Pasco Basin sediments.

Category:Geologic formations of Washington (state) Category:Neogene United States Category:Paleontology in Washington (state)