If you're looking for some hill climbing and elevation gain close to town, this is one of the better options. This trail doesn't have any singletrack, but is really just a jeep road that is popular with off-road vehicles, particularly on the weekends. This trail as marked heads up to the Charouleau's Gap itself and from there you can keep going on the road or branch off to other trails such as the Sutherland or CDO.
The Charouleau's Gap trailhead is located just east off of Lago Del Oro. If you're heading north on Lago Del Oro you'll pass Miraval and the trailhead is just a bit further up. From the trailhead sign/logbook, start heading northeast and the trail is largely easily followed throughout. There are numerous roads leading off from the main road, but use the Hiking Project mobile app
if you're not sure which way to go. Most of the time it's very intuitive though.
Throughout the way, you'll find loose rocks and some rutted sections. This isn't buffed out trail, but is only moderately technical. Since it's a jeep road though you can pick through the tough spots and following the fall or erosion line typically makes for the best route.
The initial 1.75 miles isn't too steep but just before mile 2 you start a pretty good climb. There are definitely sections where you'll probably be slowing down due to a pretty steep grade. From about mile 3.5 - 5.25 there aren't too many exceptionally steep sections. However, the final push up to the Gap is pretty steep. The climb up alone nets you about 2,000 feet of elevation gain according to my Garmin and the return trip adds another couple hundred.
Overall a good hill climbing route with moderately technical trail. Again, just be cautious of the ATV/RZRs and other off-road vehicles.