Let me provide a transcription of the letter as the Welsh miners did not write in the best form of English:
Springville, December 15, 1856
Dear President Young,
We find in the Fourteenth General Epistle [of the First Presidency, Deseret News [Weekly], 10 Dec. 1856, 313-14.] that you wish those that are acquainted with working in lead, iron, or coal to report themselves to you. We embrace this privilege to let you know that we are well acquainted with working in the mines and are competent of doing any part of the work in the bowels of the earth and are ready to go to any place where we can do more good than in Springville.
So we remain your humble servants:Now, all we need is to track down the response letter. (hmmm.)
Rees Davis Five Jolly [?] Welshmen
John Griffi[th] (ans. 20 Jany. '57)
John's name appears first indicating that he may have penned it himself! He had been a Presiding Elder, Counselor to Branch and Conference President Thomas Davis Giles (1820-1894) in Abersychan and Tredegar, South Wales.
And this is one more solid piece of evidence tying the family to Springville, Utah!