Our Geology Image of the Month: ‘Angular unconformity’

Angular unconformity in rocks
Angular unconformity in rocks at Beach 4, Olympic National Park. Photo: Dave Norman/DNR.

This month’s update to Washington State Geology News shows a well-exposed angular unconformity in the rocks at Beach 4, located along coastal Highway 101 between Ruby Beach (to the N) and Kalaloch (to the S), and within Olympic National Park.

An angular unconformity is created when strata that were originally deposited horizontally are then uplifted, deformed, and eroded before being covered by a later horizontal deposit. An unconformity is a gap of geologic time not displayed in the rocks that are visible.

At Beach 4, the tilted strata are made up of Miocene-aged (about 23 million to 5 million years ago) turbidite deposits overlain by weakly stratified Pleistocene ( 2.6 million to 11,700 years ago) glacial outwash deposits.

Read more in the Washington State Geology News, published by DNR’s Division of Geology and Earth Resources.

In addition to educating the public, government and industry about the consequences of earthquakes, tsunamis, landslides and other geological hazards, DNR’s Division of Geology and Earth Resources is the chief source of information about important resources Washington State, such as aquifers, minerals and sand and gravel deposits.

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