The Shirley Lake hike is approximately 5 miles round trip and is considered moderate to difficult. The first part of the trail is easy as the climb is gradual and it follows the creek closely.
Stay on the left side of creek the rest of the way up. There are some nice waterfalls along the way and the area is wooded and shady which feels great on a hot summer day.
There are some nice pools where you can rest and put you feet in the water on a hot day. The trail is clear in the early part of the hike where you are near the creek or going through wooded areas. There are also wild flowers along the path. The most striking one I saw was a Royal Larkspur that was 5 feet tall..
This is where you get ready for some real exertion. The creek goes off to the right but it is shorter to stay to the left and go straight up the granite. You will see some path markers but not much. As long as you keep going up, you can't get too far off path. This stretch is steep and hot but is a fairly short distance.
The Squaw Valley tram is off to your left along with these wonderful granite crags. An alternate route to Shirley Lake is to take the tram to the top and then hike down to the lake. I recommend taking the tram up just to see the views from the tram itself and the top of the mountain. There are several hikes at the top.
As you get toward the top of the steep granite trail, keep to the left. You will spot a visible trail again. Shirley Lake is off to your left.
And finally, after hiking down a bit from the crest of the trail, you reach Shirley Lake. After the long, hot climb, it is great to sit in the shade and have lunch by the side of this beautiful little lake. The granite outcropping that extends into the lake is a perfect place to shed your shoes and cool your feet.