Ken,
I have a coffee table FULL of various mineral specimens, pottery shards, arrowheads, axes, etc that I have picked up all over the country- TX, NM, WY, IN, OH, NJ, NC, Saskatchewan, Quebec, Northwest Territories, CA, AZ and all I have to do is look at them, or pick them up to remember exactly hwere I was and what I was doing at the time.
I can't explain it either, just know I like it and its pleasurable to do- I don't really feel a need to explain it to others or justify..I just know its a fun thing to do that makes me happy.