Google yamba.org which is york area mtb club good people. Rocky ridge and Lake redman are county parks and awesome riding. Michaux state park is about 30 mins from york city. If you don't mind driving 50 mins north there is Swatara state park and Rattling creek you can go to Samba.com for info. Swatara is 10 miles of fast Singlespeed singletrack.