Clay soil is one of the heaviest soils (properly and figuratively speaking!). It has a high density, water penetrates it with difficulty and once it has been retained, it will stay there for a long time. Being denser, clay soil is less oxygenated, so there is always the risk that the roots of the plants get harder and rot faster.
For the needs of a Colorado gardener who wants to grow vegetables and flowers that are not suited to clay soils, this type of soil is a nuisance. Even physically, it is difficult to work with: when it is wet, you need special strength to dig it; when it is dry… well, your work will become almost impossible.
Fortunately, the structure and composition of clay soil can be changed first and foremost by increasing the amount of limestone. Gypsum, crushed limestone, or plaster from demolished buildings can be sprinkled over clay soil. Lime will improve not only the physical but also the chemical structure of the soil (most plants prefer a slightly alkaline structure).
Secondly, you must add some sand. Not much! The sand will not bring nutrients to this already poor soil, but it will facilitate its penetration by water and oxygen, making it also easier to work.
Thirdly, fourthly and infinitely, an organic component natural fertilizer must be added, whether it is peat, compost, shredded vegetable, mulch or something else.