This is the only route up to get up Darley Mountain that has a trail. According to a few other people, there are 2 other routes that exist that don't have a trail that some poeple use.
However, this route is conveniently located on the top of Engineer pass. The summit provides you will a jaw-dropping veiw of the entire San Juan range. There is an old mining road that acts as the trail, but stops randomly 100 feet shy of the summit. So getting to the summit requires some exposed scrambling on dangerously loose rock. You must know what you doing while climbing this.
Getting ThereFrom Durango, head NE towards Silverton. Once at Silverton go towards Eureka. Once your at Eureka, keep going until you see a 4WD high clearance vehicle sign. You will need at least some clearance to continue. Passenger cars are not appropriate, but a standard all-wheel-drive vehicle will make it if you are careful and go slow. Continue down the Eureka Gulch Road until you get to Animas Forks. Past Animas Forks, there is a junction for Cinnamon, Engineer, California, and Placer Passes. Head NE onto the junction for Engineer/Cinnamon Pass. A High-Clearance 4WD vehicle, preferably a Jeep, is required. Continue passed the Junction until you get to another junction. Take a left onto Engineer Pass. If you need in-depth details on going up to the pass, refer to a 4WD book. Before the top you will pass a Overlook that is about 200 feet higher than the actually pass. You can park at this overlook and hike about 0.1 miles to the pass where the trail starts if theres no where to park on top of the pass. You are very close to the mountain from here.
If you do not have a 4WD vehicle, but still want to hike this, I'd recommend taking Engineer Pass from Lake City.
On you decent, make sure you find the safest route down the slope in which you scramble.