nor10 said:south central part of Pa. I am very close to Gettysburg
I went to high school in northern Chester County. Was not detecting at the time, but it was generally fertile and loamy soil that would not have presented much in the way of problems for pre-set ground balance models.
Looking at some geological composition maps, you are kind of in the middle of mild dirt country. Can always be pockets that don't match that and some areas where clay is brought in for ball fields or horseshoe pits can be challenging but they should be the exceptions.
Saw an article a few weeks ago about some knuckle heads detecting and digging in the woods skirting the battlefield but still within the park. They were arrested and are being prosecuted; as they should be. I'm sure that wasn't you!!!
Cheers,
tvr