Your friend needs to chill out and not worry; the plan to travel to the mountains will only make things worse.
Work Step by Step
Common rocks and minerals, such as the granite outcroppings, contain traces of uranium (page 619). Furthermore, in the mountains your friend will be exposed to more cosmic radiation. About 75-80% of our annual radiation dosage comes from natural sources, as the textbook says on pages 619-620. We ourselves are radioactive, from the potassium in our bodies, and from ingesting the radioactive Carbon-14 that is continuously being generated in the atmosphere. Your friend should go to the mountains to escape the rat race, not to escape radioactivity.