Not comparable since these are two different locations. But, yes, there was probably very little, if any, trash left laying about after the pro-Life gathering.
I was at the March for Life. We were at the very end of it and the streets were very clean. A small amount of normal street litter, but in essence, nothing. We picked up a little bit and I even saw a couple people standing on the corners with trash bags.
I wish I had taken a picture, but the rally area was nothing but grass after everyone left. Probably 250-300,000 at the rally.