Across the Wide and Lonesome Prairie is one of my favorite books, and definetely my favorite on the Oregon Trail! I first read this in 1997 when it came out, and I've read it many times since then.
This book tells the story, in diary form, of 13 year old Hattie Campbell. It starts out in 1847, in Missouri, when her family decides to travel with a wagon train to Oregon. There are river crossings, friendships, Indian encounters, deaths, marriages, and poisonings throughout the trip, but Hattie overcomes the hardships and grows into a young women.
This story tells history in a real and interesting way, and I would recommend it to almost all ages! If you liked this book, as I'm sure you will, you'd probably like the other books in the Dear America series, especially West to a Land of Plenty.