Does anyone know how often trains cross the holcomb trestle in oregon?
Once a day, likely at night. P&W runs a log train that transports logs from the Astoria line, over the United Railways District (the line over Cornelius Pass and said trestle) to Banks, then on the Tillamook District to Beaverton and then the OE District to Eugene for interchange with the CORP. The same log train also transports logs harvested in southern Oregon to be taken to a log yard in Rainier on the Astoria Line to be transloaded onto oceangoing ships for transport to Asia.
Not a whole lot of general freight; that typically moves using the "663/664" train that more often than not runs down the UP mainline to either Willsburg and on P&W rails to Tigard, or stays on the UP to Salem and then enters the P&W there.
I guess that for more up to date info that you check out the PNWR railfan group over at Yahoo Groups, there are quite a few folks that provide daily train reports and even a few P&W insiders that provide some valuable info. The group is member-only but they are receptive to new members.