BOOK REVIEW / NONFICTION : A Dramatic Tale of Two Men, History and Hard Politics : THE RIVALS: William Gwin, David Broderick, and the Birth of California <i> by Arthur Quinn</i> ,Crown, $25, 336 pages

A vein of narrative gold runs throughout California history, the stuff of a frontier epic, but Arthur Quinn has found his way to especially rich diggings in “The Rivals,” a chronicle of California politics in the years before the Civil War.

“The Rivals” focuses on the “uncouth” David Broderick, a transplanted New Yorker who opposed slavery even at the risk of Southern secession, and the “genteel” William Gwin, a Mississippi plantation owner who headed up a California political faction called the Chivalry, which sought to preserve both slavery and Union.

Broderick and Gwin both served as U.S. senators from California in the 1850s, as we learn in “The Rivals,” but their personal and political antagonisms ran so hot that they ended only upon the field of honor.

“Here was one son of the people who would teach this Chivalry . . . a thing or two about providence, as (Percy Bysshe) Shelley’s Prometheus taught the tyrant Zeus,” Quinn writes. “Against this Chivalry, David Broderick, with his callused hands and scarred face, would build a workingman’s democracy. Let the Chivalry oppose the Shovelry at its peril.”

“The Rivals” is a curious blend of hard politics and romantic tale-telling, a tableau of bigger-than-life historical figures that unabashedly mixes history and melodrama at every opportunity. The book is a work of scholarship, but Quinn is never shy about livening up history with melodrama.

The opening scene of the book, for example, shows us Gwin’s arrival in California by steamer on a foggy June day in 1849. All the while, the author runs up historical asides like signal flags on a masthead: the natural history of San Francisco Bay, the political ambitions of John C. Fremont, the economics of steamship transportation, even the price of a hotel room in gold-feverish San Francisco: “Four dollars a night . . . for a bad room.”

But, at the same time, Quinn embroiders the scene with sentimental flourishes that are typical of the author’s lush prose style.

“The few fog billows left on the edges of the bay . . . hovered like melting snow hills in the air or were fleeing like doomed half-hooded phantoms,” he writes. “It was the first morning of Creation, and the sons of God should sing.”

Quinn is a professor of rhetoric at UC Berkeley, and I suppose it is his scholar’s conscience that prompts him to give us a small caveat. His sources are sometimes “impeachable,” as Quinn delicately puts it, but he adopts a “welcoming rather than critical” attitude toward them.

In other words, Quinn has not been too fussy in choosing the more scandalous and uproarious stories that have attached themselves to these two historical figures and the times in which they lived. Thus, we are witness to vigilante justice as well as electoral politics, and we spend time in bordellos and barrooms as well as smoky back rooms.

One ugly truth, however, is presented with grim clarity. California, we are reminded, has always been a place where people of various colors find themselves in close and not always comfortable proximity with each other, and the politics of race that we see in “The Rivals” are disturbingly familiar.

Gwin and Broderick debated a question of policy--would California be a free state or a slave state?--but the debate was fueled by much deeper passions.

“On a single San Francisco street corner you could find a greater diversity of humanity than anywhere else on the continent,” Quinn points out, a phenomenon that some folks (including Gwin) viewed as “a humanly induced social pandemonium” rather than something to be celebrated.

“American politics as a system of rationalized hatreds” is how Quinn describes the landscape on which Broderick and Gwin feuded in the 1850s, and--tragically--his book amounts to a caution and a rebuke to those of us who live in California in the 1990s.