Clastic Dikes in Lake Roosevelt Bluffs
Clastic dikes filled with coarse sand with cobbles up to golf ball size intrude shoreline bluffs along Lake Roosevelt in the Upper Columbia River valley. The dikes show no vertical sheeting or silt skin walls, like most dikes to the south. I counted 14 dikes including those shown here in a 1.5 km traverse of a location several miles north of the Spokane-Columbia confluence. The features here are large, but sparse. If they coalesce to form networks, the polygons are very large, perhaps greater than 100m across in plan view. They instead appear to be isolated features, perhaps best described as "filled fractures".