Formula C was an open wheeled SCCA racing class originating in the mid 1960s, derived from the failed Formula Junior class. Formula C cars were very similar to Formula Juniors; Formula B was a similar class with uprated 1600 cc engines. Formula C cars were limited to 1100 cc engines. In the SCCA today, Formula Continental is the direct descendant of Formula C.
References
Formula C (SCCA) Wikipedia(Text) CC BY-SA