Whenever I write a review of a William T. Vollmann book, I'm tempted to devote my precious number of words to the author's unparalleled ambition and productivity rather than focus on the messages imbedded in the new tome. (Only one other high-quality contemporary author causes the same phenomenon in me -- Joyce Carol Oates.)

At 49 years old, Vollmann has published a staggering amount of excellent fiction and nonfiction. Just one of his projects, "Rising Up and Rising Down: Some Thoughts on Violence, Freedom and Urgent Means," ran seven volumes totaling 3,299 pages. That project alone would have taken most other authors a lifetime of uninterrupted labor. Vollmann, however, was working simultaneously on his novel "Europe Central," which ran 811 pages and, despite its learned content, was accessible enough to win the 2005 National Book Award. He followed with thoughtful, unusual nonfiction books in 2006, 2007 and 2008.

Now comes "Imperial," weighing in at 1,306 pages. At first, it seems to cover the history of the Imperial Valley, a geographic terrain at the bottom of California, with Mexico on the south, Arizona to the east, San Diego to the west and the strangeness of the inland Salton Sea in its middle. But because Vollmann is so cerebral and such a polymath, none of his books is ever about just one topic or one place.

Vollmann's version of Imperial extends beyond a confined portion of California to encompass the Mexico-United States border. Because that border is so convoluted, even fluid, Vollmann finds himself thinking through the true meaning of national borders. In the case of Mexico and the United States, does a "border" mean anything meaningful? Does it serve any purpose other than to discourage "aliens" from Mexico who want to make their contributions to the U.S. economy? Many die trying, all of them, in Vollmann's unforgettable phrase, "presumably seekers of illegal self-improvement."

Beyond the original thought process of Vollmann, readers will find unusualness on nearly every page -- unusual use of language that occasionally comes across as cryptic but more often as poetic, unusual use of structure given the 208 chapters divided into 13 parts with titles such as "Contradictions," "Climaxes" and "Dissolutions," unusual first-person interventions into his narrative.

More predictable is inclusion of long-simmering, perhaps eternal, controversies -- illegal immigration from Mexico to the United States, the ethics of using migrant labor to fuel U.S. businesses, the question of who owns scarce water and how the water should be allocated, to name just a few. Completing the book is akin to obtaining a Ph.D. in sociology, and well worth the tuition.

Steve Weinberg is the author of "Taking on the Trust: How Ida Tarbell Brought Down John D. Rockefeller and Standard Oil." He lives in Missouri.