Basically, what Rick said - my legs are not good for more than 100 kms. Actually he's been flattering by ommitting the word "flat". By the way, the Bear is not an exception. In theory it is a century, but for me it is more like 4 rides of 25 miles each. I spend about 50 minutes at the rest stops on that ride.
Anyway, the Alpine 60-miler has close to 6,000 feet of climbing - more than enough for me.