From the passenger car park at 10,460 ft., hike on up the road (or drive if you have 4WD) to the upper trailhead parking at 10,800 ft. Follow the trail toward Highland Mary Lakes. The trail will take a decided turn west a little below 11,600 ft., crossing the creek and will again turn abruptly south above 11,800 ft., to follow the west for of Cunningham Creek to one of the first lakes. At this last turn to the south, leave the trail and hike west up the tundra & grass drainage toward a saddle SW of "Sugarloaf." Cross the saddle on tundra and talus, then drop down into Spencer basin losing perhaps 300 feet in elevation. Cross the mostly tundra/grass basin (when we did this hike, it was almost all snow here - so tundra & grass is an assumption) heading towards a saddle east of Pt.13,409. A grass-covered slope grants access to an upper bench at 12,900 ft.
You can make a choice here. 1. Drop down into Arrastra Basin, losing perhaps 300 feet to where the steeper terrain mitigates some below the 13,409 - Kendall ridge. Then gain that ridge at the first saddle south of Kendall Peak, just above the Titusville Mine ruins. Expect plenty of rock below the ridge and regaining the ridge. If you're here early season, you may get lucky and find most of this covered in snow making traverse very easy. Ice axe will be useful. 2. Hike to the summit of Pt.13,409, then follow the connecting ridge NW and N over to Kendall Peak. The initial descent off Pt.13,409 will be rocky and difficult. The remainder of the ridge will be easy enough on a mix of tundra and typical San Juan scree and rubble. Or - "Furthermore" on LoJ reports finding a trail from the saddle at 12,900 feet that contours below 13,409 on its north side and leads back over to the low point saddle between Kendall and Pt.13,409, avoiding the rubbly mess. In his photos, the trail would apparently cut through a lot of scree and talus.
From the summit of Kendall Peak, you may want to contemplate crossing on over to the west and tagging the official high point of Kendall Mountain which is Pt. 13,338. It's about .8 mile away. We chose to not follow the ridge on over that day because of time constraints and because of a difficult looking notch just west of the Kendall Peak summit that appeared to offer a 3rd class scrambling problem. On LoJ, "Futhermore" reports an attempt to negotiate that notch unsuccessfully and has a photo of it. If you don't continue on over to Kendall Mtn, then return as you came. Returning through Arrastra Basin may be a more attractive option with an opportunity to view wildflowers, etc.
Alternate route: If driving or walking up from the passenger car park at 10,460 ft., just before the road crosses back over to the east side of Cunningham Creek, there's a mining road that heads off to the right and switchbacks up the mountainside to a mining claim at 11,300 ft. Beyond the mine, the road deteriorates to more of a trail that climbs all the way into the upper bowl of Spencer Basin, close to Mountaineer Creek. From there, you could follow the route description above. This approach could save over a couple of miles and some elevation over our suggested route, however, there may be a private property issue with this approach. Use at your own risk. National Forest maps show private holdings in this area.