My favorite route
For first timers: There's basically no signage. I highly recommend parking at the "Tails and Trails" dog park, taking the trail to your left when facing the dog park, past the gate and down to the railroad tracks. To get to my favorite place to drop in: Follow the double-track next to the tracks up the hill for about a mile or so until the gravel road crosses over the railroad tracks and through another gate (The grade isn't too steep since it runs parallel to the tracks). From there, you'll see a singletrack entrance on your left. From this location, and depending on your pace and route, you'll have about 20-40 minutes of fun, sprawling, mostly-downhill singletrack. There are tons of forks in the trail, but most of them lead to the bottom. There's a lot to explore and plenty of time to get lost, but just keep moving and you'll find the bottom eventually.
I would not take new mountain bikers here - this route is somewhere between blue and black as far as technical difficulty as well as being very fast and steep in many sections. The trail can be pretty treacherous with blind corners, sudden drops, and unforgiving hillsides you don't want to topple into, so use caution on your first few laps until you get to know the trails. The space is generally pretty deserted, but I come across hikers every now and then, so keep that in mind while you're blasting down the trail.
The trails themselves are in pretty good condition, but it's obvious they aren't actively maintained as you'll come across some parts that just feel like they're falling apart. Over the summer it was very loose and dusty, and I've yet to ride this trail in the fall so I'm not sure what the drainage situation is going to be.