There are several maps of where in the state the vegetation types are, or historically were. The classic study is the map of 15 different kinds of vegetation. A smaller copy appears above, and a link to the image is below. Remember – when it comes to images, link, don’t lift! http://www.okatlas.org/okatlas/biotic/vegetation/duckfletcher.htm
A more simplified (12 vegetation types) but more clear map, in pdf format is at http://www.forestry.ok.gov/Websites/forestry/Images/Ecoregions.pdf
There are other maps on this blog – geology, etc. Just search to see what you find that you can use in your classroom!