Terry,
According to Mark Simmons, he never really learned to read or write. As an NDN agent to the Ute and Navajo, he dictated all of his paperwork to an assistant. If I remember correctly, it was a source concern for his superiors and occasionally an opening for corruption. An unscrupulous assistant could change orders or put completely different orders in front of him to make his mark on. I know this was a source of trouble and frustration for Kit. The man wasn't slow by any means he was apparently fluent in English, Spanish, Ute, Navajo, Cheyenne, Flathead, plains sign language and probably others. However his inability to read and write caused him no end of difficulties in his forays into the mercantile business, mining, and government work. Kit was a great man, but not a great business man or bureaucrat.
Interestingly enough Kit wasn't much of a self promoter either. He dictated his life story. Can't remember the name of the fellow who did it right now, but he found Kit's version somewhat needing spice and added quite a bit of 'seasoning' to it. When the final product was read to Kit, he pronounced it a pile of bull and tall tales.
Although it doesn't cover Kit's years as a trapper in depth, I highly recommend picking up a copy of Simmons' book "Kit Carson and his Three Wives". Simmons has spent decades researching the man and has a real handle on who he was.
Sean
PS Its not about polygamy.