I spent two weeks this August doing pretty much the same thing there and the Colorado Midland, too. I wasn't aware the Watertown Canyon road was no autos. I got to the gate and WTF?. So I went down to Sedalia and came up to the mountains on 67 to Sprucewood, then down the Nighthawk branch to South Platte Hotel. The Nighthawk branch is very scenic as well, don't miss this one. The ROW east to the Strontia Springs reservoir is a hiking trail (colorado trail).
From South Platte, you aren't too far from Dome Rock and Westall monument, the road is the ROW all the way to Buffalo. The road skipps up for a little bit, then you are on the ROW again for a little bit to Pine. You can see the ROW to the left below the road easily as is it mostly farmers trails. You will lose it there for a bit until you get to Crystal Lake road to the west. Then the ROW from Cliffdale, Crossons, and Estabrook is private land. No real access from Estabrook to Bailey, either.
From Bailey to Grant, Webster and Kenosha, you can see the ROW off the road closely to the river. Below Kenosha, the ROW is to the west of the road, you can see it pretty clearly all the way down to Jefferson, altho it crosses to the other side of the road. Follow the ROW, I think the power lines are right on the ROW. It'll be on the north side of the road for about halfway to Como, but it will cross and loop south for a bit then back to Como proper on the east side of town. Most all of the ROW is easily seen in town there. From there north, the ROW is to the right of the pass road until you come to the dredgings of Tarryall creek, then you loop across the valley onto the ROW all the way to Boreas and Breckenridge. I guess that's not Platte Canyon, so enough with that route.
Obviously, Google maps is your friend here. The Delorme's atlas is good, too, for quick reference on the road. If you want more detail on ownership, you'd have to look at county plat maps and go from there for permission for individual access.
There was a great restaurant/bar right on the main drag in Pine, I can't remember the name, but they were real nice and had awesome food and good micro's on tap.
Go slow and have fun.
Scott
