Unexpected tire wear--anyone see this before?

[TexasCamper]

While on my trip to SD and ND, I regularly checked my tires. I didn't see anything unusual on the leg from Custer State Park (SD) to Little Missouri State Park in western ND.

Entering the state park involved maybe one mile on a dirt road. When I arrived at the campsite, I saw that the TM's right tire (passenger side) was stripped bare at one spot. I suspect the right brake siezed and I dragged the tire a bit.

The tires are 15" Goodyear Marathon, 3.5 years old with 15,000 miles on them at this point. And the TM left tire (driver side) still looks great. I use a tekonsha brake controller.

Now since this was the first time I drove on a dirt road (actually, probably limestone gravel), I am suspicious that the brakes siezed somewhere here.

So what do you think would cause this?

-John