Check the bottoms of the feet for a round black scab. If you see one then it is bumble foot.
While waiting for a reply, I went out and took photos. Yes, it is bumblefoot. I read in the Chicken Health Handbook that they should not be bred since they would be likely to produce more that are susceptible. One of them produced a scab that went all the way through the web of the toe. I wiggled the bump (on top) and pushed the black scab on the bottom, and the whole thing came out, leaving a hole in the foot web that is healed around the edges, no blood. Weird. I have not seen bumblefoot before. The soil is very hard and rocky here in the pens. I think it is really hard on their feet. I have gone back and forth trying to decide which is better, just leaving it bare and rake out the droppings (which dry very fast in this climate) or put in some sort of ground cover and not rake it out as often. I like to compost everything that comes out of the pens. We can't really use the deep litter method here since it is so dry. Everything just stays there, it does not compost. When it does rain, whatever I put in the pens gets packed down, nothing stays fluffy. You would think the chickens would fluff it up, but they do not. The feed stores charge $7.50-$8/bale for straw around here, yikes!
I am also in a very dry climate and just moved my micro-flock into a larger coop (4x8 for 7 layers) and when I moved them out of the two smaller coops they were occupying I found the composting had begun, but it would have been probably another year before I had anything I could point to and call it compost, so it's all going into the compost pile to finish. In the run I just let them run on the dirt, but what I have is like dust, not hard and rocky, and I just rake it out every couple of weeks. They free range at least three full days a week, and an hour or so after work. If you have hard, rocky soil, you might try putting keeper boards around the perimeter of the run and putting in a few inches of sand, screened dirt, decomposed granite, or even shavings. Straw always packs down, I never had much luck with it and have read that most people have had a similar experience of it. You could also try hay, which is unbelievably expensive this year.
Sorry about the bumblefoot, hope it heals quickly.