It is formed by the natural radioactive decay of uranium in rock, soil, and water. Naturally existing, low levels of uranium occur widely in Earth's crust.
Radon is colorless, odorless, tasteless, and chemically inert.
Once produced, radon moves through the ground to the air above. It can be found in all 50 states. Unless you test for it, there is no way of telling how much is present. The Surgeon General has warned that radon is the second leading cause of lung cancer in the United States.