Crazy the difference a year and a half can make. In the spring of 2011, Foster the People was a little-known quantity making its first trek to Denver for an intimate show at the Walnut Room. The band returned to the Mile High City for a notably larger gig at the Bluebird Theater later that summer, then literally exploded on radio with the breakout single "Pumped Up Kicks." This week, the group is returning to headline Red Rocks. Red Rocks! That's a pretty stunning trajectory, no matter how you look at it. But whether this ends up being the band's peak really depends on what it does from here. A ubiquitous hit single brought the group this far, but that pumped-up track has since lost air. Is there more where it came from?