Most people start from the Stevens Gulch trailhead, which is northeast of Grays/Torreys. Follow the Grays Peak trail to the 12,200-foot level. At this point, you will come close to the saddle between Kelso Mountain and Torreys Peak. From here, proceed 1/4 mile north to the saddle. Look for abandoned (or maybe not) mining buildings here. Kelso Ridge is the 1800' northeast ridge of Torreys.
This TopoZone map
Proceed directly up Kelso Ridge from the Kelso Mountain/Torreys Peak saddle at 12,400 feet. You will initially encounter some class 3 scrambling over good rock. If you are uncomfortable with this section, turn around and use the other trail, because you will encounter similar, if not harder climbing...1000 feet later.
For the next thousand feet after the first class 3 section, the route is mainly class 2 without serious exposure, though it is wonderfully airy. The crux occurs around 14,000', when you encounter a very solid 40-foot class 4 buttress. The gully can be traversed via a rotten gully to the south. Soon after the buttress, Torreys' famous knife edge appears along the ridge, where a vein of quartzite bisects the granite. This knife edge literally comes to a point no wider than a couple inches in places, and has spectacular exposure on both sides. After a single highly exposed class 3 move to exit the knife edge, the remaining 200 yards of the route ascends a loose 30-degree, north-facing scree slope.
You can descend the usual Grays peak trail if you do not wish to downclimb.
An ice axe may be useful for the last 200 feet of the climb during winter/spring.
Exposure-averse climbers may desire a rope at two sections: the class 4 buttress and the knife-edge traverse. In either case, a half (30-meter) rope with a few nuts will suffice for both climbing and rappelling. The class 4 buttress will accept rappel slings easily, but you must bring your own, as I have seen none in place on the route.
Be forewarned: this ridge is exposed and remote. If you get caught here, you may have to downclimb. Those pondering a downclimb of this ridge after ascent of another should familiarize themselves with the cruxes. In my opinion, the route-finding is not taxing.
If you have information about this route that doesn't pertain to any of the other sections, please add it here.