The obverse abbreviation "G.S.L.C.P.G." stands for "Great Salt Lake City Pure Gold". However, an assay of the various Mormon gold issues performed at the United States Mint in 1850 showed the coins to be underweight and debased. The gold for these coins came not from Salt Lake City, nor anywhere else in Utah, but from the gold fields of California!
Sources and/or recommended reading:
"Private Gold Coins And Patterns Of The United States" by Donald H. Kagin, PhD
"Walter Breen's Complete Encyclopedia Of U.S. And Colonial Coins" by Walter Breen
Riverboat Collection - Heritage 4/2014:5453, $235,000
Riverboat Collection - Heritage 4/2014:5451, $64,625
Riverboat Collection - Heritage 4/2014:5452, $111,625