Angel's Staircase has long been the premier alpine mountain bike ride in Washington State, and it's time for it to be a premier trail running route. Here part of the description from MTB Project:
"Angel's Staircase is a physically demanding, epic loop that takes you far from civilization, so bring plenty of food and water and make sure that you carry tools that you know how to use. The rewards are fantastic views of jagged mountains and into beautiful alpine basins filled with flowers, trees, and small lakes.
"Epic" has been heavily overused, but when it comes to mountain biking the Methow Valley, this word is used more often than not to describe the Angels Staircase Loop.
This is THE Methow Valley Ride for the serious mountain biker. It requires fitness and an adaptive attitude. The loop reaches altitudes of 8000 feet so being prepared for varying weather anytime of the year is necessary. This is an all singletrack ride that takes a full day, but what a day it is."
A version of this Angel's Staircase route was run as a race for several years in the mid-2010s, but it was dropped after being too consistently disrupted by fires, heat, or other unsafe conditions.
https://www.mtbproject.com/trail/5183409/angels-staircase-loop
https://www.evergreenmtb.org/trails/angels-staircase-uno-peak#info
The Sawtooth Ridge Slam is another route in the area of Angel's Staircase, but the Ridge Slam stays more on the ridges and is slower and more difficult scrambling, while Angel's Staircase is faster and on the trails. Both are good routes and great ways to explore the best terrain east of Lake Chelan!