[Mick]

To my quick scan, I didn't see any duplicate high schools. Surprising to me, given how talent tends to get concentrated at certain powerhouse schools.

Well, even football factories like De La Salle only produce a few NFL alums, one QB and in their case, no QBs that make the list:
https://www.pro-football-reference.com/s...d=93b911c2

And you get schools like Long Beach Poly, with 58 alums in the NFL -- but no quarterbacks.
https://www.pro-football-reference.com/s...d=93b87f5a

And you get schools like Mater Dei, with three NFL quarterbacks, but none of them played long enough to merit the list (Matt Barkley, Matt Leinart and John Huarte). None had more than 19 starts:
https://www.pro-football-reference.com/s...d=93b8f152

Here's the link to all California high schools with NFL alumni:
https://www.pro-football-reference.com/s...s_state=CA

BTW, and FWLIW, I think the list is pretty accurate. My high school, which is now closed, had produced exactly one (1) NFL player, a guy who played for Utah State, then played for the Rams during the strike season. I checked, and yep, he's on the list. 6'8", 290 pounds as a high school sophomore that I used to go up against every day in practice. Incidentally, he did well enough that the Rams asked him to join the regular roster, then he failed the physical (narrow vertebrae).

[Mick]

To my quick scan, I didn't see any duplicate high schools. Surprising to me, given how talent tends to get concentrated at certain powerhouse schools.

Well, even football factories like De La Salle only produce a few NFL alums, one QB and in their case, no QBs that make the list:
https://www.pro-football-reference.com/s...d=93b911c2

And you get schools like Long Beach Poly, with 58 alums in the NFL -- but no quarterbacks.
https://www.pro-football-reference.com/s...d=93b87f5a

And you get schools like Mater Dei, with three NFL quarterbacks, but none of them played long enough to merit the list (Matt Barkley, Matt Leinart and John Huarte). None had more than 19 starts:
https://www.pro-football-reference.com/s...d=93b8f152

Here's the link to all California high schools with NFL alumni:
https://www.pro-football-reference.com/s...s_state=CA

BTW, and FWLIW, I think the list is pretty accurate. My high school, which is now closed, had produced exactly one (1) NFL player, a guy who played for Utah State, then played for the Rams during the strike season. I checked, and yep, he's on the list. 6'8", 290 pounds as a high school sophomore that I used to go up against every day in practice. Incidentally, he did well enough that the Rams asked him to join the regular roster, then he failed the physical (narrow vertebrae).