RASH above ankles after hiking long distance?

I hiked 10 miles on Saturday and noticed a bright red rash above the ankles. It started to fade, but then I was walking about 8 hours on Wed and it is now up my legs (it is still above the ankles) and is very bright red. Minimal itch. Looks more like a hickie would look like, only in big blotches and very intense looking. I am a little worried as I am backpacking about 10 miles this coming weekend. It does not look like a contact derm.