From the Oroville Mercury Register:
“Butte County may soon have a better idea of what lies beneath its surface, thanks in part to the Kingdom of Denmark. Starting in late November, a helicopter took off for several days from the Orland airport to fly a pattern over an area between Chico and Orland, and southeast into Butte Valley. Dangling beneath the helicopter was a hoop loaded with devices that created a weak magnetic field and instruments that measured how that interacted with layers beneath the soil.
Christina Buck with the Butte County Department of Water and Resource Conservation explained that underground there are layers of sands and gravels that hold water, divided by layers of clay and silt that block water passage to different degrees. … ”
Read more from the Oroville Mercury-Register here: Butte County: Helicopter survey should aid groundwater planning