I run this trail on a regular basis. I start my run where Arcade Road and El Corte meet. There is a driveway and a trail that branches off to the right. This trail eventually meets up with the actual Jim Green Trail a little under .5 miles in. You have to go down a rather steep incline and through an opening in a chain link fence to access the main trail. It is a beautiful dirt trail with nice views of Atascadero hills and the Chalk Mountain Golf Course. It is very hilly and as a runner it is a good challenge (meaning it kicks my butt every time). I wish it were a bit longer so that I didn't have to run on the streets to get my distance in (I do a 5k). It is a well-used trail, but not crowded. A lot of horses use the trail and many people walking their dogs. Unfortunately I have run into quite a few people who do not keep their dogs on a leash, which I get, but I really don't want your dog chasing me regardless if you think he or she is nice/friendly :/
This trail was very confusing, if you're doing for the first time, as far as knowing which way to go and when to turn back because the riverbed is riddled with dirt bike trails and horse trails that criss cross all over the place. There are two trail heads - one on Cortez (park and cross the rail road tracks) and one on Aragon. The Atascadero Trail Guide shows and distinct loop, but the path on all trails is more of a backtrack. The first time we tried this we started at the Cortez trailhead and veered right at pretty much each junction, trying to follow the path on All Trails, until it finally dead ended and we had to turn back. This way was really kind if neat as it passes by a neat abandoned and rusted out 50's era car, and then takes you to some fresh water pools which at this time has ducks, small fish, and tadpoles. The trail continues even further, but you would have to cross water, so it may be more for horses at that point. If you want to do the 1.7 mile loop as shown on the Atascadero trail guide then follow our second track, being sure to turn at the waypoint- it's only after you make the turn that you'll see the trail marker.
The trail starts and finishes with more shaded, wooded areas, but the majority of it is fairly exposed. In the warmer months is probably best as a morning/evening walk.
I just finished the trail for the first time. My daughters were ready to turn back at the half-way point, so I didn't get to see the whole thing. I thoroughly enjoyed it. I loved the shade through much of the trail. Those oaks are beautiful with the Spanish moss. I was a little concerned about the pot-holes in the trail. If you're not careful, you'll twist an ankle. Overall, a very nice trail. You forget that you're near civilization still.