The trees cannot be seen, because they are physically, I'd say, about 35-40 feet lower in elevation than the Arch itself, let alone the little rise on the grounds. The back edge of that crowd is on this rise that's about 2/3 of the way to Memorial Drive from the Arch. That's where my sister and I sit for the fireworks on the 4th because it gets a breeze.
Those trees are ornamental and they aren't that tall.
Thanks for all your comments, coming from someone who knows the area. They are very helpful in putting this whole event into context.
It looks like a beautiful city, from these photos.
Do you recall if the Pope drew a crowd that large when he was in St. Louis?