John,
Your photo location shows the train leaving Ambrose station/siding about to drop down the 2.2% of Howard's Gulch to Canby. The crossing is Loveness Road, and you were probably standing on CA 139. The south switch is just pass the crossing.
Not diatomaceous earth, but perlite trucked from a quarry near Paisley for Cornerstone Industrial Minerals, a partner in the new operating company. Goose Lake Railway is the new operator that took over the Lake County lease on September 9th, though leased SW 2422 took its time in arriving. LRY, LLC (dba Lake Railway) ceased operating their UP lease between McArthur (end of track), through Alturas yard and to the UP interchange in Perez. UP made it clear they had no interest in ever going to Alturas again, so Goose Lake Railway will be headed to Perez next week.