San Carlos is a canton in the Alajuela province of Costa Rica. The capital city of the canton is Ciudad Quesada. San Carlos was created on 26 …San Carlos is a canton in the Alajuela province of Costa Rica. The capital city of the canton is Ciudad Quesada. San Carlos was created on 26 September 1911 by decree 17. San Carlos has an area of 3,352.33 km² and a mean elevation of 340 m.