It varies with geology yes, produced by the radioactive decay chains of U-238 and Th-232. https://www.pnas.org/doi/10.1073/pnas.2408084121 https://www.pnas.org

It varies with geology yes, produced by the radioactive decay chains of U-238 and Th-232. https://www.pnas.org/doi/10.1073/pnas.2408084121 https://www.pnas.org/doi/10.1073/pnas.2408084121 If I recall correctly it can accumulate more readily in basements, so that's another factor. The house I grew up in had an exhaust system installed due to elevated radon levels.