This is probably more for the NW but we had fun taking a radiation detector cruising this year to check levels after the problems in Japan
. We'd take it on hikes and climbing etc....And yes, areas with lower rainfall have lower readings. Next year we'll check Indian Island and Bangor for fun!
On another note, I still prefer paper charts
but if you have computer tech savy kids
get them to set up a laptop
with a GPS antenna
and download the free charts
available for the US. A GPS antenna
cost less than $30......