I happened to read in the same week accounts of the revolution in Paris (of which I, like most Americans, had been mostly ignorant) and of the discovery of gold at Sutter’s Mill—and realized that these two world-changing and essentially accidental events had happened almost simultaneously at the beginning of 1848. That struck me as a fascinating coincidence, so I started wondering about how I might invent characters and a story that would be propelled by both events. As I started researching the period, I became more and more amazed by all that was happening then, by how the world was being turned upside down in so many ways all at once: by the industrial revolution, brand-new technology (telegraph, railroads, photography), feminism, utopianism, mass media, advertising, bohemianism, abolitionism, immigration, booming cities, wacky “new age” fads, Marx, Whitman, Poe, Thoreau, and on and on. And the United States in 1848 had just fought (and won) its first elective and first foreign war, against Mexico—which seemed especially resonant now that we’re engaged in another elective foreign war. As you say, the era is fairly virgin territory in American fiction—in our popular imagination generally—and that got me even more excited. I came to believe that 1848 really was the moment that modern life was born.

You’re so right. It was the most deadly war we fought before the Civil War, and it turned a huge chunk of what is now America into America, including California. Several future Presidents (and many soon-to-be-famous generals) fought in it—and Congressman Abraham Lincoln and Congressman (and former President) John Quincy Adams spoke out against it passionately. I think our collective forgetfulness is due mainly to the fact that it lacked any noble purpose. It was a more old-fashioned, un-American war—not for liberty or justice but for land, period. So we’re inclined not to think about it too much. And the present Mexican immigration mess