Growing up on a farm/ranch in eastern Colorado in the late 60s and early 70s, my father and I would occasionally find a sonde/balloon. Sometimes on our fields/pastures, some on neighbors. We'd be driving down a country road and see something odd in the distance, stop and walk out to it and collect what we could. They were easy to see since that part of the country is bare of trees and the land is relatively flat. Dad would send the sonde in and I had a parachute attached to a wooden hoop to play with. We probably found one or two a year. I don't recall all the details but I'm pretty certain the ones we found were launched from Denver.
With the proliferation of GPSr availability, if the data was posted somewhere, there's definitely an upside for savings some goverment revenue (i.e. taxes)