Marty, I'm not all that familiar with the outer end of the PS&P, but the inner end around Centralia is very accessible and provides some decent photo opportunities:

Blakeslee Junction, on the northwest side of Centralia, is where the PS&P, ex-NP line and the Tacoma Rail, ex-MILW line cross. There is a third line, a stub of the former UP line to Aberdeen, that also branches off here. The location is accessible from the Harrison Avenue interchange of Interstate 5, and lies to the north of the factory outlet complex and just to the west of the Interstate.

PS&P has a small yard northwest of the junction, and you can usually find a mix of power here, including BNSF and UP locomotives. You may also find a string of locomotives parked on the stub of the former UP line; UP interchanges unit grain trains for the Port of Aberdeen with PS&P here and often parks the power on the stub track to await the next outbound unit train from the port. PS&P also parks its power here.

PS&P, being a RailAmerica property, has the diverse mix of locomotives from different RA short lines. Over the years, I've seen units in RA red/white/blue, PS&P or California Northern green/white, ex-SP units in grey/red, ex-NS black/white, and ex-BNSF Cascade green and "pumpkin". You may also see lease units from HELM and HATX. The RA and lease company power is usually four-axle.

Just north of Centralia on the old Pacific Highway (Harrison Avenue west of I-5) is a newer industrial park that is just east of the PS&P line. The access roads cross the PS&P at grade and also provide some decent photo locations.