Yup. Good place for a quick ride. This is 2 miles from my house. I usually ride through on my way over to Lewis Morris or Patriots Path. It's fun leafy and loose. I still have yet to try the disc golf course there.Watnong Mountain is in Morris Plains, and it's that mountain you see the water tower and ugly condos on top of when coming down 10 West. There is a Parsippany park called Mountain Way Park in the middle of the mountain, and the southern portion is technically part of Greystone Park/Central Park of Morris County. There's a playground, frisbee golf, pond, and also like 3-4 miles of trails. Certainly not a destination, but for anyone that lives in the area it's not a bad spot to ride your bike to. It's about a 25 minute ride over there on the road for me, so when I only have an hour and a half to two hours to kill and I don't feel like driving to Wildcat, I ride over there from my house.
There is virtually no information online about these trails. Picture the Tourne but with two peaks and singletrack trails going up and down both peaks instead of a shitty gravel road, and that's basically Watnong. It's tight, climby singletrack and it's really fun, there just isn't a lot there.