Tectonics, volcanoes, mountains, oceans, beaches, erosion, lakes and rivers. Where to start? Mines and gravel pits. Mines have slag heaps and tailings. When they are mining copper for instance....they are not looking for malachite or thompsonite or agates. Beaches feature lots of rocks. The waves erode them and some of the minerals get exposed. You have mountains. Rivers and melt water expose underlying minerals. Gravel pits expose rock, did it up and pulverise it. There are mountains of rock in one place.
I live in a rock paradise. There are not many gems but I have been to exposed fault lines where there are gems in the rock and you can chip them out. The copper mines have been worked for millennia. I have dug for specimens in the tailing heaps, I have walked the beaches looking for them. Alluvial flows from glaciers deposited them. If you learn how to spot them you can find gems there.
Nice place to start would be your local rock shop, a university, a mineral club or type in gems in Maine into your browser. Great thing is you get out and look for what you like.