Answer the following question given this paragraph: 

A lava plateau is made of a large amount of fluid lava. The lava flows over a large area and cools. This creates a large, flat surface of igneous rock. Lava plateaus may be huge. The Columbia Plateau covers over 161,000 square kilometers (63,000 square miles). It makes up parts of the states of Washington, Oregon, and Idaho.


Q: When lava flows over a large area and cools, it creates a large, flat surface of what type of rock?


A:
igneous