I am not a chemist so I'm not going to give specific amounts of radon; different countries use different units. My question: why do some areas have more radon? For instance, Australia has a spreadsheet of all locations and their radon levels. I've looked it up and where I used to live, nearby, has half the listed Radon levels of where I live now. Wikipedia was a bit general to me for American examples:
Iowa has the highest average radon concentrations in the United States due to significant glaciation that ground the granitic rocks from the Canadian Shield and deposited it as soils making up the rich Iowa farmland.
So it is rock or soil types or weather or something else that causes the different amounts?