Sometimes the best thing for soil is just to leave it alone. If you are installing a xeriscape, you might not need much in the way of soil amendments. Waterwise Mediterranean plants and a lot of Utah Native Plants don't thrive in rich soils and prefer the sandy or clay soils that already exist in our area. On the other hand, if you are building a vegetable garden or other beds with plants that are "heavy feeders" then you will need amendments to enrich the soil.
One thing that is highly recommended is to get a soil test from Utah State University. This is a great way to get some information on what exactly you have in your soil.
Another thing that is recommended is to research the plants you have chosen for your xeriscape. Find out what type of soil they require and group plants with similar needs together. Then you can adjust your soil accordingly for that zone.