I see that you are calling these marks ridge marks. the proper term for this is reed marks. the reeded edge of coins digs into other coins and makes the impressions.
Thank you, I didn't think it was anything important, just a mystery to me, I just noticed them on many of the quarters I was checking and couldn't figure out what was making them. It seems they're much more prevalent on quarters though, rarely do I see them on other coins. Thanks for clearing that up for me.