How often did heavy SP power make it to Willits, and did any make it to Eureka?

I know they tested the SCL U36B Mate slug set there, but what else showed up? Blogs seem to indicate that any SDs and U33Cs did show up in Willits once in a while, instead of the usual SD7/9s. There was a substantial weight difference, with SD7s and early SD9s only weighing around 169 tons, and later SD9s around 179 tons, while later 6 axle units were typically ballasted to around 200 tons.

See Pic of heavy power at Willits

Is this the wye at Willits? It's been so many years, I don't remember. If so, how in the world did U33Cs and an SD39 (last unit another SD39 or SD40) end up there? In 1979, weren't the SD39s pretty much assigned to working Bakersfield to LA, helpers and locals out of Mojave including the Lone Pine Local? I seem to recall seeing them in SLO, so maybe they worked the coast also. I don't recall U33Cs being used much in Northern California. Was this an empty lumber block that originated at Taylor or COI that ran straight to the NWP with LA power? Seems unusual. Was this road power or a helper set to get out of Willits with a loaded train?

I was in So Cal in 1979 so this is outside my personal experience. Any comments with better information appreciated.