The first oddity I saw was a microphone about 3 feet off the ground, on the side of the road just after the last house, before getting to State property. It has a large metal base, with a huge cable leading to a suitcase size box chained to a utility pole, and appears to be powered by a solar panel.
On the base is a title "Aberdeen Test Range Environmental Sound Meter" which must be for a study being conducted by the U.S. Army at the "nearby" Proving Grounds. I found a 1993 study titled " Measurements of Blast Noise Propagation Over Water at Aberdeen Proving Ground, Maryland" but that is over 10 years ago. I can't make out the phone number on the plate, so I'll need to go back [I went back - it is 410-278-8605]. Here's the base's main web page: http://www.atc.army.mil/.
I pick up trash, recyclables and other detritus on most of my hikes. Usually, by the end of a weekend or week-long camping trip I have a gallon-sized plastic bag of odd novelties cast-off by society. The plastic fishing line is difficult to see in this scan, and the 2 larger pieces of hard plastic are unidentifiable, but the laser cleaning box yielded a serviceable CD/DVD case.
The audio tape is cracked and useless, and the title is probably illegible on this image, but the tunes are a commercial product from the 1999 release Esperando Un Angel by Banda Arkangel R-15.
Each 4 mile walk was just around 1 hour. Saturday was raining slightly, but Sunday was sunny. On the latter, I went around the main park loop, seeing cardinals, bluejays, and a red-headed wood pecker (I heard several others). Just before getting back on the main road, a herd of 8 or so white-tailed deer bounded away from my trail. I now have ideas for the next Scout nature hike.