Delphinium geyeri is still very common around Denver, especially in the hogbacks just West of the city. There are incredible stands near Fort Collins and Boulder as well. For almost a month in June this blazes the most amazing blue color. It is a dryland plant that must grow in sparse prairie grasses, preferably on clay soils and have a relatively dryish summer to really do its thing. It can get 4' or more tall--so rock gardeners may think it's too big...but every rock garden should have a wild garden and meadow nearby!
I have seen much dwarfer forms of this in the Wyoming steppe: sometimes barely a foot tall. Of course that may be environmental. It is not an easy plant to grow in containers and takes several years to reach its full glory.
This is a plant that has established in the Plains Garden at Denver Botanic Gardens. I have two good specimens I keep forgetting to photograph in my Westridge garden...
Just look at that blue....aaaaah! Only a few penstemons and meconopsis can match that piercing color!