How long has the Wasco vs. Shafter Cali High School Rivalry been going on for?

There's no widely documented, specific start date for a "rivalry" between Wasco and Shafter high schools in California in the way that some high school rivalries are historically tracked. While the schools are geographically close and likely have competed athletically against each other for many years, it's not a rivalry that's been formally recognized or extensively documented in the same way as, for example, some longer-standing and more intensely publicized rivalries. The intensity of competition between the schools likely varies from year to year and sport to sport.