Beans are a warm season crop and are tender to frost. Wait until chances of frost are past before planting your beans. In Salt Lake and Utah valleys, mid-May is usually considered "safe" to plant tender vegetables.
Beans germinate best when the soil temperature is between 60 and 85 degrees F. If your soil is warm enough, you can go ahead and plant your beans before mid-May. Then, if frost is possible, cover the bean rows with a floating row cover or frost blanket to help hold the ground's heat in for the night.
In the USU Extension publication "Home Vegetable Garden: Variety Recommendations for Utah", the last page holds a table of recommended planting dates for most vegetables.