I wanted to thank Dallas, Chris, Bob, Mike, John, steamfan77, for all the comments and all the other likes in regards to my mud work on the trackside repair scene with crane and truck! I got the idea from watching videos of trackside repairs such as, freight car wheel/axle replacement, knuckle replacement, truck replacement, brake jobs, etc. on real railroads, like CP, BNSF, CSX, UP. Noticing that the rail equipment, both rail car and repair equipment are pretty grungy and dirty (grease, oil, mud, rust, dirt, hydraulic fluid, etc.), and the mechanics seem to be camouflaged in the same stuff!! If you work on the railroad, it's best if you don't mind getting really dirty!
I have family that live in the Sierra Nevada foothills on the California side, and there is tons of red clay mixed in with sand and gravel. When I went up to Paradise, the town that burned down in the camp fire in 2018 to visit what was my Dad's property, I grabbed a freezer bag full of the red clay and brought it home. So some of the red clay on my layout is from that property and serves as a memory of the many times I visited Paradise and my Dad.
So I used the same bag of red clay to muddy up the crane and truck. I just used white glue and sprinkled the dirt onto it and then shook off the excess. With white glue I can always take some HOT water and remove the dirt if I so desire.
Once again, thanks, and wishing you all Happy Holidays!