Is copyright in a book, researched and written by a man during a
course of a marriage, community property under the laws of California?

The wife didn't participate, per se, in the book's authorship.  (Of
course, she fed him, etc.)  The husband worked outside the home; the
woman didn't.  The book is unrelated to his work.

(Not that it matters, but the book is a history of the small town
where the man's family settled 200 years ago as immigrants.)

Hello.

First of all, I should note that, as always, Google Answers provides
general information and is not a substitute for professional legal
advice. If you need professional legal advice, you should contact a
qualified attorney in your area.

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Yes, under the case of "In re Marriage of Worth," 241 Cal. Rptr. 135
(1987), the copyright in a book written by one spouse during a
marriage is community property in California.

See:
"In re Marriage of Worth" (1987).
...Moreover, the Act expressly provides for the transfer of a
copyright by contract, will "or by operation of law."   . . . 
Consequently, notwithstanding that the copyright "vests initially " in
the authoring spouse . . . the copyright is automatically transferred
to both spouses by operation of the California law of community
property..."
http://www.studentweb.law.ttu.edu/cochran/cochran/Marital%20Property/worth.htm


Additional reading: 

"The leading case on this issue is Marriage of Worth 195 Cal. App. 3d
786 (1987). In Worth, the husband and copyright holder of a book
brought a suit for copyright infringement against a third party after
he divorced his wife. His wife alleged a half interest in any proceeds
from the infringement lawsuit because the book was created during
marriage in California, a community property state. A California court
held that the wife was entitled to her half of the infringement award
because the copyright was earned during marriage and was part of the
married couple?s property. The federal copyright law did not preempt
California community property distribution of copyright proceeds."
source:
But Who Gets the Intellectual Property?
Janeen Vilven-Doggett, J.D., Ph.D., cached by Google:
http://72.14.207.104/search?q=cache:d_DHIkduwQQJ:www.viennapat.com/newsletter/vol5iss5/butwhogetstheip.htm+%22+In+Worth,+the+husband+and+copyright+holder&hl=en&gl=us&ct=clnk&cd=1


"Only one court has squarely addressed the relationship of copyright
and community property law. In re Marriage of Worth, 195 Cal. App. 3rd
768, 241 Cal. Rptr. 135 (Cal. App. 1st Dist. 1987). Under Worth, a
non-author spouse holds a share of all copyrights vesting during the
marriage. In addition, Worth holds that federal copyright law does not
pre-empt state community-property provisions. Worth, 195 Cal. App. 3rd
at 776-78, 241 Cal. Rptr. at 139-40."
http://www.dkslaw.com/papers/cracking.html

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search strategy:
"copyright is community property" california
"marriage of worth" copyright "community property
://www.google.com/search?hl=en&lr=&client=googlet&q=%22marriage+of+worth%22+copyright+%22community+property&btnG=Search

I hope this helps.