It is called "River Road Park" and is in Hamilton county at 126th and River Road. It isn't close to you, but it might be worth the drive. Here is the description from the HMBA website:
"Thanks to Hamilton County Parks Dept. we have access to a new trail within River Rd Park at 126th & River Rd. This trail has been built along the White River with access near the south canoe launch or one of the two overlooks off of the paved multi-use trail. It has been designed and built according to IMBA standards for a "Gateway" trail. A Gateway trail is usually near an urban area and designed to introduce people to the sport of Mt. Biking. This trail is nearly a 1 mile loop with an upper and lower trail built above the seasonal flooding of the White River."
I asked Jonathan about it yesterday and while he said he has never seen it, a friend of his built the trail. It is not long at all but that provides more control over how far/long to ride. I am going to go look at it sometime this week, it is supposed to rain so I can take an umbrella and not waste riding time hiking it :)
I posted a question
here asking how it compares to Pine Loop. The person who answered my question mentions Town Run as well but I've been told by everyone I know/trust to avoid Town Run at this time. They said isn't like other mountain bike trails and it would be better to drive to BCSP instead.
There is a new trail opening at Fort Ben, but I've not heard how it will be classified.