The gentlemen whose names are written in the title of this brief posting all have written about explorations of the west. Lewis and Clark left St. Louis in 1804 at the request of President Jefferson. Irving never made the complete trip but wrote a daily history, based on journals and correspondence, of adventurers who helped his friend John Jacob Astor establish his western fur business. And Francis Parkman wrote about the Oregon Trail, having spent some time living in the west and studying Indian life.
I have read Parkman and thumbed through Lewis and Clark a number of times. Now, having visited Washington Irving’s home recently, I picked up Astoria and am about 2\3 through that 700 page book.
I am not sure why, but I find them all fascinating.