Mountain Biking

I'll be visiting ft Collins in early August and renting a bike. What are the best trails to check out around town. I'll be working until about 5 PM so the trails need to be reasonably close to the city and 2 to 3 hours in length so I can make it back before dark. I expect to have 3 to 4 evenings available.

I'm an intermediate rider. I will likely be renting a Ripley or Ripmo. Any suggestions on what trails to check out (or where/what bike to rent) are appreciated.