Steep. That's the word for this climb. But is the high point on Box Ridge called High Box or Hibox? You decide.
Start at the Rachel Lake trailhead (off I-90 at Kachess Lake).
Hike two flat miles up Box Canyon. Pass through a couple of slide zones. In the forest immediately after the second big slide zone, look for a path leading off the trail.
The path goes through forest and rock bands, very steeply uphill. It pretty much disappears once it breaks into grassy goat meadows. (At this point memorize where you came from, as there is a cliff band to negotiate on your way back.)
Ascend the meadows and pick up the path again as you reach talus. Work your way under the summit rocks around to the right, all the way to the southeast ridge. From here, follow the ridge up to the summit. Patience is required, but careful routefinding will avoid any exposed hard climbing. Only a few class 3 moves, on generally solid rock. But test the holds before you commit to them.
A loop can be done by running the ridge over to Lila Lake at the base of Alta. I have not done this, so I can't report on any difficulties.
Descend the ascent route or make the loop.