Front Range clays have the advantages of holding water well and being naturally fertile. Their tendency to compact is less favorable for plant growth. Organic amendments shoulder aside tightly packed clay particles to make space for the air so critical to plant root growth. Sandy Front Range and mountain valley soils drain freely, eliminating plant growth problems from too much water. Organic amendments added to sands act like a sponge to hold enough water for plant growth.
Organics also hold fertilizer nutrients - another item often lacking in sandy soils.
Rocky, well-drained, mountain soils benefit from organic amendments in the same manner. With lawns and perennial plants you have a one time opportunity to amend before planting. With annual plantings like vegetables, you can amend the soil every year. Take advantage of opportunities to amend soils with organic material, then carefully regulate the amount of water applied for best plant growth. By doing both, you will realize the greatest results from your gardening efforts.