I think I would like to do the Santa Barbara Red Rock 40 Mile Endurance Run.
I took a look at the cutoff times and the 20 mile cutoff is only one hour faster than I'm able to walk with my backpacking gear on. If I run the downhills, I ought to be able to do it. If by then (November) I can run more than just downhills, so much the better. I think it would be really fun.