Most training programs recommend not going farther than 20 miles before the marathon. My longest run so far was 20.25 miles on the marathon course. The uphills and the downhills were dramatic.
I've heard St. George Marathon runners say that by the end of the race your legs are pounded to a pulp by the last half of the marathon with the steep downhills.
I've had the pleasure of running up the Veyo Hill twice now. It seemed to extend up into the clouds. I expected Jesus to greet me at the top of the hill. My legs felt like Cool Whip. Although the second time was much better, on my first attempt I thought I'd never reach the top. See if you can find the Veyo Hill on this St. George Marathon elevation chart:
"The marathon is kind of like the Ph.D. of public fitness accomplishments. There are very few times as an adult that you can go out and do something that's authentically difficult and be publicly lauded for it." ~ Cate Terwilliger