Renton Formation

The sandstone is weakly cemented, most commonly with calcite, but in places matrix silt and clay act as the binding agent.

Some beds in the formation are very soft and plastic when wet, owing to the weathering or alteration of feldspar to a montmorillonitic clay.

The Renton formation is a nonmarine arkosic sandstone and siltstone, with carbonaceous shale, and noted for its Muldoon coal seams.

[1] Lidar-Revised Geologic Map of the Des Moines 7.5' Quadrangle, King County, Washington |url= https://pubs.usgs.gov/sim/3384/sim3384_pamphlet.pdf= 4 May 2020

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