Yes! I have that book. It's a great read authored by Candice Millard. Teddy was defeated in the 1912 election and was humiliated by it. He, his son Kermit, and a famous Brazilian explorer (among others) ended up mapping an un-named tributary of the Amazon. It was a one thousand mile journey. They went through hell is the best way to put it. Teddy almost commited suicide. They lost canoes and supplies to whitewater, endured starvation, were attacked by natives with poison arrows, ravaged by disease, there were drownings, and they went through a murder within their group.
Pretty cool you mentioned that book...