Colony Days is Atascadero's main civic festival, held the third weekend of October. It centres on a Saturday morning parade down El Camino Real, followed by a day of food stalls, classic cars, and live music in Sunken Gardens. The Tent City re-enactment on the Friday evening commemorates the original 1913 colony arrivals who lived in canvas tents while houses were being built.
It is the right weekend to be in Atascadero if you can choose. Otherwise the same Sunken Gardens stage hosts the Summer Saturday concert series (free, June through August) and the Christmas tree lighting in early December.