Headed back down:
On the way toward the park exit I got a flat -- I think this was my hardest-to-fix-flat ever, requiring 4 attempts:
1. First, I couldn't get air in the spare. I thought the valve was bad, but we discovered when we returned to the shop that the spare tube had a hole in it (maybe I did it when changing tubes?).
2. Luckily I had a patch kit. But the first patch didn't hold (I was using too large a patch).
3. 2nd patch held, but after I put the tire on the bike it started losing air. I took the tire off and inspected the tube and again and found...
4. A second patch on the same original tube (!). Still not sure how it got 2 holes in it; again, maybe I created a hole while remounting the tire on the rim. So I used a 3 rd patch to fix that.
Whew! That was a tough flat.
The loop out to the canyon and back is about 35 miles...I took off down another highway for a bit and then headed back, in all the ride for me was about 40 miles.
Great weather, great ride.
There are at least a couple of stores that do these day rentals w/fairly nice bikes -- the other I looked at was Las Vegas Cyclery, not far away. Both also organize mountain bike rentals out to the same area.
Was a great way to spend a day, will certainly do it again.