Monolith Festival, Red Rocks Amphitheatre Saturday, September 12 and Sunday, September 13 | Details | Read more Now in its third year, the Monolith Festival is on its way to establishing Denver as a music fest destination, a la Southern California/Coachella and Chicago/Lollapalooza. This year, the cultivated two-day lineup features headliners The Mars Volta and Yeah Yeah Yeahs along with Colorado indie bands Boulder Acoustic Society and Danielle Ate The Sandwich. More: Cool Kids | Tesla | The Gaslight Anthem | Wavves | The Get Up Kids