West/N.West of OKC is very flat. The further you move east the more terrain you have including the Ouchita Mts (http://en.wikipedia.org/wiki/Geography_of_Oklahoma#mediaview...), the Arbuckle Mts (http://en.wikipedia.org/wiki/Arbuckle_Mountains#mediaviewer/...), and the Wichita Mountains (http://en.wikipedia.org/wiki/Wichita_Mountains#mediaviewer/F...).

Now none of these hold a candle to the spectacular geography of Western Colorado, but they offer nice reprieve from the office for nature lovers. And plenty of lakes for those that prefer swimming, sailing, etc.