logging truck 1921, I'm wondering how they got those logs up onto the truck, push? pull? roll?

notice the plank road, necessary to get the heavy truck with the skinny damn tires out of the woods. It's been a while since I posted about plank roads, but what little I learned about them never mentioned them used for logging, and I bet it's due to the ignorance of the logging world by the rest of the driving world that was interested in getting across the sand dunes

http://www.blackdiamondnow.net/black-diamond-now/2013/04/coal-creek-lumber-co-circa-1921.html

1920
http://www.blackdiamondnow.net/black-diamond-now/2013/04/early-log-trucks.html