What makes Carhenge special is that it's made of cars, 38 of them, rescued from nearby farms and dumps. Reinders noticed that the monolithic dimensions of cars from the 1950s and '60s nearly equaled the stones at Stonehenge, and he built his monument with a 96-foot diameter to match the proportions of the original.
A year earlier, Bill Lishman had the same idea and built a similar Autohenge south of Port Perry, Ontario. But there's no indication that Reinders and Lishman knew of each other. It seems to have been a case of two creative thinkers separately having the same revelation at roughly the same time.
Three foreign cars were originally part of Carhenge, but were subsequently dragged away, ritually buried, and replaced by models from Detroit (The foreigners' grave at the site is marked by another junk car). The "heel stone" is a 1962 Caddy.
After a couple of summers the Reinders family spray-painted the cars a flat gray to make the monument look more like a Stonehenge. It's carefully maintained so that it doesn't suffer Autohenge's fate.