I have weekend field work and was doing some preparation research for my ventures with the idea of a little side trip to this area of odd features in the LiDAR imagery. I have done some work in this area in the past and would like to tie a few odds and ends from past field notes together and follow up on a few features I have come across in the area.
LiDAR (Jefferson County)
The site is in Jefferson County on the east side of Discovery Bay. The general landscape has been glaciated with glacial scour traces on the landscape from north to south. But the topography in the central portion of the LiDAR hints at some other types of features. The geologic map indicates the presence of bedrock and fault contacts between bedrock units in vicinity.
(Schasse and Slaughter, 2005)
This part of the Schasse and Slaughter (2005) map directly incorporates the mapping of Gower (1980) including the areas mapped as landslides in bright yellow. Em are different units of siltstone, conglomerate and sandstone and Qgt is glacial till. There are some volcanic units as well including some possible adakite adakite-and-tamanowas-rock. The LiDAR lineations that are at an angle to the glacial striations might be the result of resistant layers of rock and how they are oriented, or Maybe something else?
I am familiar with the coastal area on the map. My own interpretation of the landslide mapped areas is that they are not landslides. There are a couple of minor smaller shallow slides on a portion of the slope but nowhere near the extent indicated on the map. Gower (1980) provides no explanation and Schasse and Slaughter (2005) provide no details specific to this area and in other areas of the same map perhaps overly used Qls. Gower's main interest as best I can tell was the bedrock and perhaps there was something he saw I did not.
All the above said, the little bit described above is a bit of an example of the information gathering that takes place when this (me) grunt geologist heads out to do field work. I will also rely on past field projects in the vicinity as well as an older paper only map I have of the area (Hansen, 1976) and mapping done even more recently to the southwest by the USGS that includes a much greater detail of late glacial units and interpreting a number of landforms that appear in the LiDAR of that area and may be applicable here as well - part of my purpose for visit. Off to test as many explanations I can think of see what I can see.