The Meysan Lakes trail starts from the last Whitney campground before Whitney Portal (at about 2400 meters of elevation). You have to park the car on the road and walk through the campground, looking for the trailhead that is actually hidden among summer homes. If you start hiking before sunrise, this is not trivial at all. To make matters worse, the trail crosses the paved road one more time: walk a bit uphill and look on your right for the second start of the trail.
Parking area:

The trailhead is off this road hidden in the campground:

The trailhead:

The trailhead:

Very long switchbacks (that will be very annoying on the way down) take you around the wall in front of you and into the valley created by the creek that comes down the lake. The trail ends at a meadow. Continue in the same direction (roughly south) and enter the lake from the west.

Mt Irvine is the prominent peak to the west of the Meysan lakes but what you see from the lake is a false summit.

Looking south from the lower lake:

Looking west from the upper lake:

Mt Irvine can be climbed from the western side of the lake along a class-2 chute that terminates exactly at the summit. The same chute can also be used to reach Mt Mallory.

The other way to reach the summit (not recommended unless there is snow/ice in the chute) is via the southeastern ridge, which is a series of false summits. Leave the trail just when the trail starts going down towards the lake and climb the mountain to your right. That is the first of many false summits. A tiny pass leads you to the western side of the mountain and now you can see all the other false summits. The real summit is in fact barely visible. You have to follow the crooked ridge created by these false summits until there are no more peaks to climb! It easily takes 2 hours from the first false summit (the one you see from the lakes) to the real summit.

The route viewed from Mt Russell:

• Meysal Lakes trailhead
• Grass Lake and leave the trail: 2 hours
• First false summit: 3.5 hours
• Mt Irvine (4197m): 7 hours

One can also climb Mt Irvine from Arc Pass via Consultation Lake (possibly the easiest route) but that requires a Whitney Zone permit. The bureaucracy that is paid to protect you has a unique way to make simple things complicated and dangerous.

Routes:

Video from the top of Mt Irvine