Lidar measurements now indicate Milwaukee to have only 297 feet of prominence, thus removing it as a ranked summit. Nevertheless, you will likely want to go over Milwaukee in order to reach Pico Aislado. There are two difficulties in describing our route to Milwaukee Peak. The first has to do with the 1967 Crestone Peak quad which shows a trail that leads from near Upper Sand Creek Lake to a pass (Milwaukee Pass) just north of the Milwaukee summit and between it and a northern sub-summit. On that quad, that trail is in a drainage separated from the headwaters of Sand Creek by a prominent ridge. This trail does not seem to actually exist any longer. It appears that a trail route now follows more in the Sand Creek headwaters and comes out at the Milwaukee/Marble saddle. In addition, when we did this climb, as mentioned before, there was so much snow, locating any trail was impossible anyhow. So you might want to supplement our description with the G&M description of Pico Aislado and a report by Ryan Schilling on SummitPost here:
We have sequenced Milwaukee with Pico Aislado and also Marble Mountain. Leaving Marble for another day can easily be done if this 3-peak sequence is too much for one day or weather forces a discretionary retreat, which is what we SHOULD have done. As for our route, because we wanted to avoid snow and willows as much as possible, from a camp location at the end of the long meadow at 11,060 ft., we headed north, first cutting through forest, then hiking along the edge of the forest and took a wide-swinging arch path to the NW, gradually ascending on mostly tundra. At one point we had to cross some talus slopes with rocky rubble, after which, there was a steeper gain into the head of Sand Creek, followed by more tundra hiking (we assume) to the saddle between Marble Mountain and Milwaukee Peak. This route is shown on the Google Earth image by a red line. On the map we supply, we show both possibilities, though most everyone seems to use the trail to the Milwaukee-Marble saddle.
From this saddle, head SSW following the steepening ridge crest on tundra and rock. We crested the false summit north of Milwaukee and picked up the trail coming up from the Cottonwood drainage which we were able to follow for about 100 yards, but then left it to continue along the ridge to a saddle (13,300 ft.) followed by a notch mentioned by G&M and Ryan. Drop (i.e. - downclimb) into the notch and then the challenge begins. It's not that far to the summit, but it won't be easy. Literally climb a short section of rock wall (4th class) and then locate the ramp/ledge that goes south along the east face of the peak. It's very obvious. The ledge is narrow and exposed and can be intimidating for some. This is the crux. We found this ledge to be similar to the ledge you follow on the east side of Pyramid Peak, before you begin the final, more vertical ascent to the summit, but far less extended. The ledge led to an obvious trail that switchbacked up about 20 feet onto steeply pitched rock and tundra ledges. We climbed upward another 30 feet or so before finally reaching terrain where it felt safe to stand and walk. That's the end of the 4th class section. Regaining the summit ridge, from here, stroll/clamber on to the true summit.
Many if not most climbers, once they top Milwaukee will want to continue on over to Pico Aislado. From Milwaukee, you have a clear view of the route over, so as you rest and munch on your lunch, plot your ascent over. From this perspective, Pico Aislado is very impressive and a little intimidating. To descend Milwaukee, return as you came, but keep in mind that from the Marble-Milwaukee saddle, it's easily possible to hike all long the ridge over to Marble Mountain and then drop back down to the camp location at 11,060 feet.
Links to other information, routes & trip reports for this peak that may be helpful.