SP - Snodgrass Slough Bridge
Photo taken by Douglas Butler in September 2016
View this photo on Flickr
BH Photo #366126
I have been able to locate very pictures of this bridge, given it's location along the line. Here's a link to one photo of the center column (for the swing pivot).
Per State of California details, the remaining piers/pilings of this bridge were removed between 1984 and 1988.