"Just received an offer from California," Crosthwaite told Scout.com on Thursday night.
He told Scout.com earlier this week that he felt his offer sheet could be changing soon.
"I have six offers but we've had a bunch of schools come through the last two weeks and a couple of schools are coming to watch my spring ball this week," said Crosthwaite. "So if everything goes good, I could have a lot more offers."
The Cal offer comes as surprise as the Bears had not been by the Cathedral Catholic camp before Thursday's offer.
"It's a tough one to figure out who could be my next offer," Crosthwaite said earlier this week. "The offensive line coaches from Oregon, UCLA and USC all said they would come and watch me this week. Oklahoma is interested, too. That's about it right now."
USC and UCLA are area schools he has interest in, but he is not limiting himself to schools solely out West. "I'm open to anywhere right now, I don't really have a top five," said Crosthwaite. "I want to see some more schools in the summer and then senior year I'll decide.
"It doesn't matter to me where it's at. I'm going to take trips to schools that have offered me. It doesn't matter if it's a school on the other side of the nation or close by. I'm considering everyone."
Crosthwaite competed at the Stanford Nike Camp this past weekend, and he plans to camp at UCLA and USC this summer.
Academically, he reports a 2.8 GPA. He will take the SAT in June.
Stay with CalSportsDigest.com and Scout.com for more on Alex Crosthwaite's recruitment.