The region where Glass Mountain belongs to is Red Bed Plains.
Answer: Option A
Explanation:
Glass Mountain is in the south west direction or area to the United States and is in the north mid area of Texas. This also confines to the south mid area of Oklahoma.
Red Bed Plains have been named after the surface strata made up of rock which is red in colour. It has the Glass Mountain which is typically not a mountain but a few metres of stick out physical feature with mesas and buttes.