. . . . Is this road or off-road? It is not rural, it is not urban; it's in the green area - but green area is not defined! So, what is it? . . . .
It's the middle of the desert, that's what it is. The green on that map is probably the boundaries of Anza Borrego Desert State Park. Don't let the color on the map fool you, there is not a lot of greenery out there.
Actually, Fish Creek Wash does show up on my Garmin maps, and is shown on all of the paper maps I have as well. I think even Sandstone Canyon shows up on all my maps. From the end of Split Mountain Road the route is unpaved. It is generally an easy trail, probably rated 1 or 2 on scale of 1-10, with 10 being the most difficult. I strongly suggest 4WD because of a few spots where there is soft sand right before some rocks, and 2WD tends to dig holes in that sort of situation.
A couple of years ago the first response to the Fish Creek run thread was something like "Why such an easy trail?". As in "why can't we go someplace challenging?". Well, I happen to like this place, and since I'm setting it up, I get to choose where. In the end, everyone said they had a great time, even though it was not at all challenging or technical. Maybe they just said that because they didn't want to hurt my feelings. Or, maybe driving though a slot canyon maybe 10 feet wide and 150 feet deep in places was pretty cool. If you want to see what it looks like there is no shortage of pictures here and on my blog.
Since you brought up the question "is this road or off-road" I will take this opportunity to remind everyone that the rangers do take quite seriously the concept of staying on the trail. Even though Fish Creek is pretty wide in places, this is not an OHV area, and we are expected to stay on the established trail, and not cut new tracks across the desert, even if only for a short distance. Paul can tell you all about how I had to talk the ranger out of arresting him last time. (Okay, maybe not arrest, but he did threaten to cite him.) It was an interesting conversation (and thank you again to whoever it was who pointed me out to the ranger), and it may well have been just a combination of an inexperienced ranger and a lot of people out there. In Paul's defense, I didn't think he had done anything wrong either.
Basically this will be a nice leisurely drive (with stops along the way) up a sandy Fish Creek Wash until we find a suitable lunch spot, then we'll go explore what is left of Sandstone Canyon. We come back out the same way, with a detour through Loop Wash on the way back if it's not too late.