What's the hardest xc course you've ever run?

I also nominate Bull Run in Hereford, MD. There is a section called "the dip" that runners traverse twice, which is basically down into (and then out of) a ravine. Steep enough that they wrap gym pads around the trees on the way down.

Mt. SAC 4 mile race in 95 degree heat. nope nope nope.

If the "Bull Run" you mean is the one where they have the Maryland state meet, then that is definitly a very tough course. My favorite part is that there is a steep downhill with a slight turn and a tree at the bottom. When I ran it they had padding around the tree because someone apparently ran into the tree and knocked themself out once.

The other course I would like to mention is the Salesianum course in Brandywine Valley Park in Delaware. There is one hill so steep and long, that all three times I have run this meet, I saw someone who dropped out and just sat there. One time, they were lying on the ground quivering with their concerned teammates around them. The first mile is down hill, but the finish is substantially higher in elevation than the start so there is a huge elevation gain the second and third mile.