Colorado Four O'Clock

Is there such a thing and what is it used for? Is there another name for it?

A check of various books in our reference library failed to turn up anything by that name, "Colorado Four O'Clock." There is a family of plants called the Four-O'Clock family, also known among botanists as the Nyctaginaceae. According to Britton and Brown's "An Illustrated Flora of the Northern United States and Canada" (Dover, 1970) the Four-O'Clock family is represented in the United States by several species of Allionia, Abronia, and Tripterocalyx. It is possible that one of these species is known locally by the common name "Colorado Four O'Clock" because some of these species are known to grow in Colorado.
Timothy Johnson's "CRC Ethnobotany Desk Reference" (CRC Press, 1999) indicates that several species of Abronia – known commonly as "sand-verbenas" – have been used for a variety of medicinal purposes. For example, A. fragrans, has been used for gastrointestinal disburbances, mouth ailments, and skin ailments by the Navajo. A. elliptica was used by the Hopi as a sedative and for children's ailments. Allionia incarnata, also known as "trailing windmills", was used by the Navajo and the Seri for diarrhea, fever and skin ailments. Tripterocalyx wootonii was used by the Hopi and the Navajo for children's ailments, snake bite and throat ailments.
To complicate the story further, at least one species of evening primrose (Oenothera biennis) is known as "four-O-Clock". The evening primroses have well established medicinal properties which you can read about in the Richters catalogue.