I really appreciate all the responses I've gotten. I'm not claiming to be an expert at this, but I have stared at the frame and thought about it a great deal, and I'm convinced it's a buckle. There is a crease that cuts across the frame at 90. It's not a round or oval dent that might be caused by something pointy hitting the frame. The fender strut looks to be in pretty good shape, by the way. That could have buckled if there was a hard collision between the frame and the strut.

I'm scrapping the frame. I freely admit that I could be wrong about whether that is really necessary. However, I figure if there is even a 5 or 10% chance that the frame is unsafe, it's worth spending the bucks to replace it. (I'm probably buying a $200 Fantom CX frame from Bike Island + LBS labor). I feel I got off lucky this time. Broke the foam in the helmet, but avoided a concussion. My knee is hurt enough to miss probably 3+ weeks of cycling, but at least the doctor thinks there are no torn ligaments or tendons. Next time could be worse. So maybe I'm wasting money, but I'll least I'll have a little more peace of mind.

Thanks everyone!

I can't speak for others, but there's never a need to justify a personal decision to me.

Sadly, what was lost in this thread was consideration of what caused the accident in the first place. You mentioned brake shudder, but didn't say how bad it was or how often you felt it. Anything that cause poor modulation of the front brake can be serious (much more serious than a dented frame), so when you build the replacement make sure that the front brake is smooth and predictable. You might consider using a crown mounted cable hanger, which has been known to reduce shudder.

Best of luck for a speedy recovery, and a long season of great riding on the new bike.

Brake squeal and shudder was sort of a struggle with this bike. I went through a number of iterations of trying to solve these problem(s), which would go away but were never permanently fixed. I played with pad toe-in to varying degrees, different pads, adding a brake booster, and tightening the headset. Ironically, I recently purchased a crown-mounted cable hanger but hadn't installed it yet.

In the days prior to the accident, I noticed that I was starting to get shudder again, but only when braking hard. When the accident happened, I wasn't braking hard. I was going down a steep hill, but I was really just feathering the brakes to keep from going too fast. Then I felt a couple of pulses in the brake lever telling me it was starting to shudder, then I was flying through the air. My instinctive reaction to shudder has always been to let the lever go when I felt it starting to happen, so I'm 99% sure I didn't brake harder. I can't think of anything else that would have instantly locked the wheel. Once I had a fender get caught up in the tire of a different bike and had a very similar accident, but nothing got stuck in the wheel his time. I can't really explain why it happened, but the lesson learned is not to take any more chances with this type of behavior....