Methinks it might not be the most representative of California's political history.
California is just California, and trying to apply an "Anglo" lens is dumb and ahistorical.
It's true that Spanish influence isn't taken into account enough in this article, but the article is still pretty sound in the importance it puts on Puritan and Borderer (Scots-Irish) cultural influence, as these are the two foremost cultural forces at odds with one another to this day, not just in California, but across the United States. The Okies in this case would be Borderers.
And again, although we see other non-Anglo cultural forces, immigrants typically align and integrate more or less with either the Puritan or the Borderer ethos.
The book examines a variety of folkways, naming conventions, and lineages in the cultural regions throughout old England, discovers those same things present in regions throughout America, and then follows the continued expression of those folkways and lineages all the way up to the present day.
And although we can find similarities between Puritans or Borderers with other cultures around the world, we can't make a convincing case that, for example, the Japanese had a significant influence on American culture and politics, because again, the primary sources revealing the folkways examined in Albion's seed are quite distinct and can be accurately traced from old England, to American settlement, and again up to the present day. Puritan architecture, food, naming conventions, and ancestry is quite distinct and well-understood, and we see evidence of those things throughout the United states, whereas there's not much Japanese architecture, food, place-names, or influential dynasties here in America.
Anyway, Albion's Seed is a very good book that I highly recommend reading.
Okies were not uniformly Scotch Irish - it was a generic term for internal migrants from North Texas and Southern Oklahoma which was very ethnically diverse with German, Czech, Russian, and Southern settlers along with Native Americans and Hispanics.
Irish (eg. Kearny), German (eg. Haas, Levi, Sutter), Southern Italians, Russian, and Chinese settlers were much more prominent than Anglos during the frontier era along with the obviously large Hispanic population in a region that has been under Spanish rule longer than it has been under American rule.
There's a reason why bock bier (eg. Shiner Bock), dryland farming (a Russian German thing), frybread (from the Bureau of Indian Affairs era), Cowboy culture (a merger of older Hispanic Ranchero culture with southern settler culture), etc became a thing in Texas and Oklahoma
(and to your point about italians: I'm not sure but suspect the use of snubbing posts in round pens came via swamp italians. Also, don't forget the portuguese: not as prominent as on HI, but still pretty common, eg Devin Nunes)
During my 20+ years in the Bay Area I listened to a lot of Portuguese/Azorean radio, so much that it corrupted my accent. I was born in the Texas of Brazil but I sound a bit like the British equivalent now.
Absolutely (though it's specifically Azoreans)!
And to that point, stereotypes do not take into account the historic diversity that Central California has had.
Mexican, Okies, Portuguese/Azorean, Italian, German, Czech, Armenian, Chinese, Punjabi, Russian, and other settlers had an outsized influence on the development of Central California.
And this itself highlights how Albion's Seed does not generalize well outside the Eastern Seaboard (nor did Fischer intend for his work to be applied that way - he only concentrated on New England, Virginia, the lower Delaware Valley/Philly, and Appalachia, not on the rest of the US.