My wife is from Santa Barbara and her family (now in Sacramento area) always has tri-tips at family gatherings. Love them smoked and cooked very slow.
Tri Tips were/are very popular with the Chumash Indians of that region and later settlers picked up on it. That's why Tri Tips are very popular in Santa Barbara. If you go to picnic areas there on weekends, at least half the folks are barbecuing Tri Tips.
Presumably we are discussing Santa Maria BBQ:
(tri-tips are traditional but the goodness can and has been extended to other cuts too...)
https://www.sunset.com/travel/california/santa-maria-bbq
https://www.zagat.com/b/5-things-to-know-about-santa-maria-bbq
https://santamariavalley.com/news/a-brief-history-of-santa-maria-style-barbecue/