[arcticfox]

That is a lot for most people. Obviously the upper bound on what's possible is massively higher, but if you take a mildly fit person off the street and put them through 4k feet & 13 miles w/ a 45 lbs pack, they'll be feeling it. An out-of-shape person would be completely destroyed at that point.

[dredmorbius]

Add elevation to this. Reds Meadow is already at 7,500 ft. I believe the 4k ft mentioned is net climb for the hike, not necessarily a peak elevation of 11,500 ft., though passes in the region certainly rise above 10,000 feet, and peaks top 14,000 (Whitney).

With a full pack, unacclimated, making 10+ miles is a pretty good day. 13 miles outrunning a forest fire is respectable.