Which takes me back to a shower thought I had a long time ago: How do you know you don't need a geiger counter unless you have one?
It cost ~$650, but that's because it uses a very high-end geiger tube, and can detect alpha and beta in addition to gamma radiation. Comparable commercial devices do apparently cost a couple thousand.
Low and behold, the desert rocks weren't radioactive. However, taking the counter on an airplane was quite shocking, and gave the cabin crew real concern.
Concern about radiation exposure or concern about the mysterious-looking device you whipped out mid flight? ;)
Realistically though most things aren’t radioactive in a meaningful way.