Conquistador by S.M. Stirling
Another alternate history book by Mr. Stirling. In this novel, a WWII Veteran, shortly after the end of the war, finds a gateway to an alternate Earth, one where Western Civilization didn’t take hold. The planet is lightly populated with people and still mostly an untamed wilderness. Most of it takes place in California, and what would be California in this alternate world.
A fun and exciting read, with a nifty Sluggy Freelance reference near the end.