The easiest approach to Mt Gayley for a day hike is from the South Fork trailhead west of Big Pine via Glacier Notch.
This South Fork trail starts at the Glacier Lodge (2300m) and reaches Willow Lake in 6.5 km at 2900m of elevation. You don't see the trail because the pass is above it, and there's a forest in between. The trail then descends into the valley and reaches a fork. Turn right at the sign following the direction for Willow Lake, but don't go down to the lake. Cairns can be confusing. Head west up the drainage of the Big Pine/ South Fork creek. The trail ends right way.
The nicest way to coast the South Fork creek up from Willow Lake is to stay on its southern side, after crossing the tributaries coming down from the southern peaks. A use-trails appears and disappears on that side. The northern side of the Gayley creek is all talus rock, but the route is easier to follow (so probably the best option in the dark). At the second southern canyon you should reach a little pond and then a vast meadow. This is a good point to cross over to the northern side of the creek, where a use trail leads through the now sandy terrain (steep and sandy) up the drainage.
Head west all the way past the waterfall.
The use trail
on the northern side leads to the lake below the Sill glacier. This is a
bowl with many little ridges. It is best to coast it to the right (north)
to avoid going up and down all the time. Basically, this popular use-trail
heads for Mt Gayley and continues west up the saddle between Mt Sill and Mt Gayley.
That saddle is Glacier Notch. If there is no snow/ice, this saddle is a steep
ascent on loose scree. As you approach it, you should notice a diagonal
groove. Climb that groove until it gets too steep. Then look to the left and
you should find easier ways to climb Glacier Notch.
There is an easier way to get to the base of Gayley: several of the chutes
to the right of the use-trail lead to it. So there is no need to go all the
way to Glacier Notch.
If you take the ridge from Glacier Notch, you will have to do some serious class-3
rock climbing. There is an easier way, the so called "Yellow Brick Road" that
is mostly class 2. I suggest you take it from this point (right of the cube),
which is about
on a straight line between the point where you enter Glacier Notch and the
View from Mt Gayley (2012)
View from Mt Gayley (2018)
Links:Pictures of this hike
View from Mt Gayley