official answer:

“The bloom time changes every year,” says state park interpreter Jean Rhyne. “Generally it happens early in April, but it can take place any time between mid-March and early May.” https://www.visitcalifornia.com/experience/antelope-valley-california-poppy-reserve/

我估计五月初还是有的，不过出发前确认一下。既使这里过了花期，南加五月还有很多别的盛开的野花。