Shelf Lake Trail is a very busy trail in summer. Lots of fishermen on their way to Shelf Lake to catch some cut throat. The summit sees however a lot less traffic.
Plan your trip during the week if you search for solitude all along the trail!
From Shelf Lake Trailhead the trail is leading in a series of switchbacks up to the hanging valley of Smelter Gulch.
After this first ascent the trail levels out a bit and leads up to the treeline. After crossing Smelter Creek a steep final last ascent gets you up to Shelf Lake. This part will be very soggy, especially during the spring run off.
You will get the first view of Decatur Peak only minutes before you reach Shelf Lake. The pyramid shaped mountain you see to your right after exiting the tree line is actually only a point on the Southern Ridge of Argentine Peak.
The steep grassy slope to your left gives quickly access to East Ridge of Decatur Mountain.
The Ease Ridge gets you even quicker up to the summit - it is an easy Class 2 hike.
From the summit you can either return as you came or follow the Great Divide a bit northwards, soon steep scree/grass covered slopes will get you back to Shelf Lake.
Soon after the trail levels out a bit after the first steep ascent you will see an area with several fire rings at the lower end of a beaver pond (lots of moscitos in summer).
The next suitable camping area is at the lake - at night expect temperatures below freezing point for most of the year.
Hiking boots - walking sticks will be a great help for the several creek crossings.