I've been reading a lot of biographies lately, and find they're a great way to learn a bit of history (my history classes in school were pretty bad). I recently finished "Undaunted Courage," which is a biography of Meriwether Lewis, and am currently reading Dorris Kerns Goodwin's book about Roosevelt, Taft and the muckrakers, and I was struck by the yawning gulf between knowing nothing about anything west of the Mississippi at the beginning of the 18th century, and to having everything settled at the beginning of the 19th.
I've obviously heard about "the wild west" in pop culture, but is there a good book or biography that you'd recommend that would give me a sense of that time period?
I have a couple you could chew on. Check out Daniel Walker Howe's What Hath God Wrought which is a great overall history of the period. It also spends a lot of time on the development and integration of the West (which at that period meant the Midwest and some of the Plains). It only goes up to about 1842, though.
Another interesting one might be Cronon's Nature's Metropolis which looks at Chicago's development as a commercial hub connecting the East and the West from about the 1830s onward. Both are pretty long but accessible.
If you're looking more about stuff west of the Rockies, check out Kornel Chang's Pacific Connections, a great transnational study of the Pacific Northwest.