Why is there a man-made hill along River Road?
I checked out the site on Google Maps, which gives you the option to zoom in on satellite photos of pretty much anywhere. I zoomed in on that area of River Road and, it appears at least, the hill you're talking about belongs to some old railroad tracks. There is a set of railroad tracks running somewhat north to south about 1000 yards west of River Road in that area. Along the tracks, there is a junction that curves off to the east, but it ends abruptly before reaching River Road. You can see the barriers at the end of the tracks in the satellite photo as well. I attached two PDF images of the area below for you to take a look at. Sorry, in advance, for my poor photo-shopping skills. If this isn't the hill you're talking about, maybe the Mailbag sleuths will be kind enough to jump in and set the record straight.
(Updated 2:52 p.m.) I just got a phone call from a gentleman who participated in creating the man-made hill on River Road. He said it's simply piled-up lime sludge from Huron Lime Company. He said the lime is harmless, it was just extra from the company's operations. There is another such hill of lime in Berlin Heights, too, he said. Thanks to this caller and everyone else who is helping out with the mystery hill!