If this is a question to be directly answered from the textbook, it says "The Mormons wanted to be left alone and resisted federal authority." That means the Mormons living in Utah had conflict with the US and refused to join.
Going into further detail, the Mormons practiced slavery and polygamy in Utah. Both practices went against American morals and America refused to grant Utah statehood until the Mormons banned polygamy. The Mormons refused at first, causing the delay in statehood being granted to them.
