This weekend Aspen Snowmass is offering a summer version of their popular Audi Power of Four race series - the Power of Four Trail series. The Vertical K race up the front of Aspen Mountain takes place on Saturday, July 18. On Sunday, the signature race of the series, the 50K Ultra, which covers the four mountains of Aspen Snowmass on a mixed course of single track and dirt roads, will be offered, along with a 25K race on the Government trail betwen Buttermilk and Snowmass. Race details at www.aspensnowmass.com.