Axios Des Moines: Around 50 acres of undeveloped land connecting Des Moines and Pleasant Hill will be turned into a new mountain bike park, Polk County Conservation director Rich Leopold said Tuesday. Recreational advocates say the metro area is in need of another public park, as evidenced by a 40% jump in trail usage last year. Plus, Copper Creek Mountain Bike Park will also function as a massive rain garden to improve water quality and reduce flooding.