“As a channel evolves into ever more extreme loops, eventually two separate bends may approach one another and join. When this occurs, the river takes the shortcut and establishes a new channel, bypassing the cutoff loop. The abandoned channels, which may be miles long on large rivers, record the curve of the channel like a letter C or U. Geologists call such abandoned channels oxbows because their curves are reminiscent of the U-shaped pieces of wood that fasten the yokes onto the necks of oxen (see fig. 2.3). The emigrants-despite handling real oxbows every day-didn’t use that term. They called the abandoned channels sloughs.
When they first form, oxbows contain standing water—a haven for mosquito larvae. Over time, with no moving water to keep them scoured, these stagnant ponds fill in to become low, swampy depressions. Emigrants along the Humboldt saw oxbows at all stages, from fresh ones holding several feet of water to ones that had progressed to the swampy stage. You can see the same thing along the river today. And if you want a “period rush,” as history buffs call it—meaning that you want to transcend time and touch the past in a personal way—then wait for dusk on a summer evening along the banks of the Humboldt River. As the sun slides below the horizon, the keening mosquito hordes emerge from the thickets, proboscises armed and ready. That’s when any spark of romance that you might still feel about the westward journey winks out, and you feel only profound gratitude for living in an age of sealed windows and insect repellant.”