Ramps are the skater's natural reaction to the lack of concrete.
Back in the late '70s, ramps were the thing, especially for those who lived in out-of-the-way areas where there was no concrete to be found, other than sidewalks and streets.
See, street skating had not even been thought of yet.
Sure, we rode on the streets, but the basic Ollie had not even been invented yet! (I know - hard to believe that the Ollie wasn't always with us - I still, to this day, do NOT know how to Ollie very well!)
Anyway, the half-pipe in these photos was mostly made of wood that my friend Bret and I "acquired" from local industrial areas, late at night, as we placed the 4' by 8' sheets on our skates and "rode" the wood home!
(We were teens with no access to a car and no way to tell our parents that we wanted to take wood that didn't belong to us)
But my dad did help us build this half-pipe.
It had no flat bottom, because, again, flat bottom wasn't even thought of yet!
It was a perfect radius half pipe and it helped me learn a lot of the basics of skateboarding, like fakies, airs, (sometimes punching through the 1/8" wood on landing) and frontside kickturns...
The other ramps in my "skatepark" included a 1/4 pipe up against the wall of my house, and a wedge shaped "ditch" ramp that was really just a couple of pieces of wood leaning on top of some chairs.
So I had 3 ramps in my backyard, at one point and we learned a lot on these ramps.
Then, we graduated to hunting down pools and it was all over from there!