I'll give you a for example.
The book is Journal of Trapper by Osborne Russell, which records the author's life and adventures as a fur trapper from 1834 to 1843. Due to bad luck, it was not published until 1914, twenty years after the author's death. Like Parkman in The Oregon Trail, Russell mostly just tells us how he went about his business in an unusual place. Russell's working, not on vacation, so a lot of the book is about which river he followed, where he found beaver, and where he wintered. Until we get to page 101 of the 1965 University of Nebraska Press edition.
Russell and his comrades are trapping in what is now Yellowstone National Park. They're not working too hard. They're taking a bit of a vacation, themselves, actually, hunting and admiring the geysers and mudpots. Russell and his co-worker White are napping when:
Presently I cast my eyes towards the horses which were feeding in the Valley and discovered the heads of some Indians who were gliding round under the bench within 30 steps of me I jumped to my rifle and aroused White and looking towards my powder horn and bullet pouch it was already in the hands of an Indian and we were completely surrounded (102)
Now here, something is happening:
an arrow struck White on the right hip joint I hastily told him to pull it out and I spoke another arrow struck me in the same place but they did not retard our progress At length another arrow striking thro. my right leg above the knee benumbed the flesh so that I fell with my breast accross a log. The Indian who shot me was within 8 ft and made a Spring towards me with his uplifted battle axe (102)
Russell and White miraculously escape, but the Blackfoot Sioux have taken everything they own except for a bag of salt. And both men have been shot in the legs by arrows. They walk back to a fort on the Snake River, maybe 250 or 300 miles through the Rocky Mountains.
I guess this is only about 10 pages out of 120. Still, what an adventure. There are other reasons to read Journal of a Trapper - as an account of how the fur trade worked, it's essential, and this line is curious:
We passed an agreeable winter We had nothing to do but to eat attend to the horses and procure fire wood We had some few Books to read such as Byrons Shakespeares and Scotts works the Bible and Clarks Commentary on it and other small works on Geology Chemistry and Philosophy (109)
It's not exactly as exciting as the story of how Frederick Douglass learned to read, but the path that turns this fur trapper into a posthumous author is almost as unlikely.
The Oregon Trail is the greater book - well-written, more varied - but in Journal of a Trapper, holy cow, something happens, does it ever.