I have quite a lot of information on Dick Yager in my genealogy file. He was a "double" cousin of my Great-Great-Grandmother Margaret Watts Hays. She wrote about his death in Letter 58, 7 Sep 1864 in "The Watts Hays Letters".
" Mother you heard that Dick(57) was killed some time ago. He was not killed then but poor fellow is gone now. Oh Mother it is hard to think of, he was wounded at Arrow Rock(58) in the head. He fell from his horse, did not come to hisSelf for some time, was run over by horses, brake one leg but was getting well of his wounds when he was come upon by the D..... They murdered him in a most cruel manner(59). It nearly kills his poor old father, his Mother I fear for her for she is sick and this news will go hard with her altho she has been expecting it. Dicks wife(50) and Chile is in Texas."
There is an Index of People for each section of the Letters so you can look up the numerous letters he is mentioned in.