The main route up Aperture Peak is approached via Jigsaw Pass.
There are two primary ways to get to Jigsaw Pass. Either from Bishop Pass or from the North Fork of Big Pine Creek (see "Getting There" on the main page").
From Bishop Pass...
take the Bishop Pass trail until a point at the very top of the switchbacks, before the final ascent to Bishop Pass. Head cross country due south towards a small tarn at the base of a snowfield on the north face of Agassiz Peak. At this tarn, you should find the remnants of an old trail, which is cairned. Follow this loosely-defined route across the base of cliffs to the east, before it dumps you into a large morainal boulder-field. Scramble your way across the boulder field, picking the path of least resistance, towards the base of the chutes that lead to Jigsaw Pass. Please see the attached annotated pictures, as well as this description, at the Gendarme Peak page
Once you reach the base of the correct chute (it is the southern of the two chutes-- much more solid and less loose), head upwards. I tried to stay to the right as much as possible in the chute. At times, this yielded more solid rock/rubble. After a few hundred feet of upward progress, I found it easier to tackle the easy Class 4 rock (it's white) on the right wall of the chute. Then, there is a large, leftward-trending corner/roof above you. You should take the left fork of the chute here, on loose blocks with some solid rock underneath. Go above the overhang, and then contour back right into the main chute. The top is a bit easier, with one difficult move on the top out.
You can take any number of forks of the chute to the top-- they should all go at Class 3-4.
Secor says, "It is difficult to identify the correct chute leading to Jigsaw Pass when crossing the pass from west to east. Jigsaw Pass is south of the lowest point northwest from Aperture Peak, and is seperated from the low point by a small peak. Ascend the southern of two chutes, over scree, grass, and broken rock. The ascent is easier than it appears from below."
Detail of route up Jigsaw Pass from the Bishop Pass side.
From the North Fork of Big Pine Creek
: I haven't been this way. Secor says to go up the Fifth Lake inlet stream from Mt. Agassiz, and take the north branch at a fork. Easy terrain should lead to Jigsaw Pass, which is the lowpoint north of Aperture Peak.
From the top of Jigsaw Pass, there are two ways to go.
From Jigsaw Pass, traverse northeast over boulders for a few hundred yards, and a chute should reveal itself, going directly to the summit. The summit from this angle appears to be a wild fin of rock sticking straight up. The chute should go quite easily, with no major difficulties. If you encounter greater than Class 3 climbing, you are off-route, go back and look around a bit and you will find a Class 3 way. Or make things more fun and difficult, if you so choose. This chute leads to the NW Ridge, just before the summit. Scurry around the big wild fin of rock-- the actual summit is a rounded hump just beyond.
Northwest Chute detail.
If you like a little more spice in your life, take the NW Ridge direct from Jigsaw Pass. It is Class 4+ and quite exhilarating. Climb up steep and exposed cracks in smooth slabs to achieve the NW Ridge. Then follow the highly exposed ridgeline, across the top of several gendarmes (around them when necessary) and along a couple of knife-edges to the summit. If you decide to bail back to the Chute, once above the slabs, you should be able to traverse over into the NW Chute.
Northwest Ridge detail.