Landslide near West Twin River

We received a tip yesterday that a landslide recently became active, probably in the storms that blew through the area in mid to late November. The landslide occurred in a quarry that has been inactive for some time. The highway south of the quarry is State Route 112.

The quarry is an old clay mine that use to supply clay to the cement mills in Seattle. It is actually still owned by a cement company that has a working plant in Seattle. The report we got was the landslide had rocks that were actively rolling town a scarp and some of the pictures we received are amazing.

Photo by Dave Parks, Department of Natural Resources

Photo by Dave Parks, Department of Natural Resources

The good thing, so far this landslide isn’t threatening any houses, pipelines, powerlines, or such. If it starts progressing uphill, it could eventually impact State Route 112, but at the moment it seems unlikely. The area of the site is part of the Miocene-Oligocene marine sediments of the Pysht formation of the upper Twin Rivers Group, which is locally interbedded carbonaceous and fossiliferous claystone, siltstone and some fine grained sandstone. A clay layer within the Pysht formation at the site was mined for cement manufacturing in Seattle. Also the Burke Museum has a whale skeleton (Miocene) from this quarry, probably by Jim Goedert. The Pysht formation also contains many near shore fossils, like bivalves and gastropods. So, we will keep our eyes out for another whale skeleton (although we might need a bigger truck). Before you think this would be a great place to head out, know that this area is extremely dangerous. Rocks are currently raveling down the scarps and toe of this landslide and sections of the landslide can move and give way at any moment. It isn’t worth your life to try and collect fossils here. The ground is torn apart and you could easily fall into a covered (or uncovered) crevasse and get trapped. Sudden movement of the landslide or the snapping of tree roots could knock over trees without warning. This area is also private property and no tolerance will be given to anyone caught in this area, especially given the extreme danger that this area faces. If you would like to collect fossils from the Pysht Formation (or anywhere like that), contact the DNR Geology and Earth Resources Division, they can help you find safe and legal locations to collect on.