UPDATE: Answer Revealed
It is SELENITE! For those who guessed, Gypsum, you are technically correct. Though this crystal pictured, Selenite, is a specific type of Gypsum.
This selenite crystal was found in the the mud of a canal bank and U.S. Magnesium near the south shore of Great Salt Lake. Selenite is the name given to the crystalline variety of the mineral gypsum (CaSO4·2H2O). Gypsum is a common evaporative mineral. While gypsum is commonly mined for use in drywall (what interior surface of most building walls), the crystaline form of selenite makes it difficult to process and thus undesirable for use in drywall.
For what are arguably the most amazing crystals ever found, check out Mexico’s Cueva de los Cristales