Wood ashes are alkaline, so have a "liming" effect. My understanding is that CO soils are often already alkaline in which case it may not be a good idea to add to that, especially if you wish to grow plants that don't do well when the soil pH gets too high for them. It would also depend on how much you use - it is harder to change the pH of clay compared to sand so would require a larger amount. Do you have any problems with plant leaves turning yellowish while the veins stay green? I don't think wood ashes would do much if anything to improve the structure of clay, usually compost is the best thing for that.
