This picture is a view of the Giant's Graveyard south of LaPush on the Pacific coast of Washington. The rocks are one of the most recently accreted terranes in the Northwest, the Hoh terrane. Here on the coast south of LaPush we can see young rocks from the ocean floor that were stuffed part way down the subduction zone and then forced back up, becoming plastered against the edge of the continent. The process has broken and mingled the rocks from the ocean floor into a messy mixture of large pieces of rock surrounded by a matrix of shale; the shale itself used to be mud.

There are also layers of sediment on top of the Hoh terrane that were not accreted but instead deposited in place on the coast. They provide evidence that the coast has undergone rapid uplift in the last few thousand years, at the same time as the waves have swiftly eroded into it. This is a raw, dynamic coast that is changing rapidly in response to the continuing subduction of the Juan de Fuca Plate offshore.

Convoluted sandstone beds

This picture shows convoluted, folded, and broken beds of sandstone in a matrix of shale, part of the Hoh terrane south of LaPush. Select the image to see a larger view. Use your browser's back button to return to this page.

Conglomerate

This photograph shows a conglomerate in the Hoh terrane south of LaPush, near a fault zone. The conglomerate may have formed as an underwater debris flow that was then buried, compacted, and cemented together before it became accreted to the edge of the continent. Basalt and chalcedony, or chert, are among the types of rock that compose the rounded cobbles in the conglomerate. Select the image to see a larger view. Use your browser's back button to return to this page.

Uplifted marine terrace deposit

This photograph shows young (Pleistocene and Holocene) deposits of sediment on top of the Hoh terrane. The upper, light-colored bed, beneath the grass and thin dark soil, is loess, wind-blown dust and silt that was deposited during the early Holocene epoch, roughly 8000 years ago, after the end of the last Ice Age. Beneath the loess are darker deposits of silt and mud that were left by rivers flowing to the shore during the Pleistocene epoch. Since then, this stretch of coast has undergone much uplift (approximately 50 feet in the last 8000 years) and waves have eroded the old shoreline away, creating today's shoreline about 2 miles inland from where it was 8000 years ago. Select the image to see a larger view. Use your browser's back button to return to this page.

Melange

Here is a mixture of basalt and sandstone surrounded by shale, part of the Hoh terrane. This mixture of rocks from the ocean floor was shoved and mixed together by the subduction and accretion process. This image spans about 10 feet (3 m). Select the image to see a larger view. Use your browser's back button to return to this page.

Glossary terms that appear on this page: accreted terrane; subduction zone; shale; sandstone; conglomerate; fault; debris flow; loess; basalt