SacRT pictures were of a bridge over a slough and the UP on the Consumnes River College extension of the Blue Line. Ground conditions basically very deep alluvium and high groundwater, no bedrock anywhere near the surface.

SacRT has some interesting bridges. Most are more or less standard concrete box-girders like those used across freeways, but there are several less usual types. Check out the Watt Ave. overhead on the Gold Line, for instance, that was retrofitted rather than being built along with the original line; vertical clearance for the road couldn't be obtained with a normal box girder without moving a station, so the concrete girders are above track level. An old SP steel plate-girder bridge was reused in Folsom. The American River crossing on the Blue Line is a track laid in one lane of a freeway bridge. That's engineering - finding ways to make things work cost-effectively.