Answer:
When the Church of Jesus Christ of Latter-day Saints (commonly called the "Mormon" Church) was established, it faced a lot of persecution. Eventually the persecution became so heavy (a literal extermination order placed on them) they decided to make a trek west. Many of them migrated to what is now Utah. Also, missionary work in England brought in some converts from Europe who also traveled to Utah. Once settled in Utah, the Mormons expanded, colonizing many areas in the western United States. Many of these areas still have predominately Mormon populations.