This is the entrance to Tomorrowland, known as the Avenue of Flags. A common theme you'll notice in these pictures is flags. Apparently there were flags everywhere in Tomorrowland 1956. Also seen is the Clock of the World (middle), Circarama (left) and a Monsanto exhibit (right).
In this picture you can see the Moonliner rocket (a smaller replica was added back to Tomorrowland in 1998) with Rocket to the Moon behind it. Notice the Frontierland poster near the bottom of the picture.
The Flight Circle is seen at the bottom of the picture. There was where model planes were demonstrated (welcome to the future!). In the distance you can see the old Astro Jets and even further you can see the nice open space of Anaheim California before it was populated with mid-sized houses and cheap hotels.