I found this article on Steven Campbell Sr. in the Feb. 1926 Mining Review. I am also providing a link to Steven Campbell Jr.'s original letters on Coal Mining.
Steve Campbell Sr. hurt in mine cave in
Telephone message received here Thursday evening states, "Steven Campbell Sr. former well Known Rich Hill Miner was badly injured Thursday by cavein at Henryetta, Okla. where he is employed as a mine boss."
Mr. Campbell had almost gotten out of the mine when the cavein started but at the last moment falling rock caught his left leg, crushing it just above his ankle, causing a compound fracture. He was taken at once to the Henryetta Hosptial for teatment. It is believed that Mr. Campbell will be laid up for several months before he fully recovers from the injury. Friends here regreat his misfortune.