Her Majesty The Queen planted the first of 4,000 trees that will create the parklands - a key public event space at the Olympics.
She then walked along a section of the 100m track where the Olympics' blue riband event, the men's 100m final, will take place.
"Her Majesty was able to view the Olympic Stadium's completed external structure and the work that has started on the roof lift of this flagship venue," said ODA chairman John Armitt. "Planting the tree today is the first step in the creation of a new green space that will reflect the traditions of great British parks and will create a fantastic backdrop for the Games and the heart of the new community in the area post-2012."
In total, over 4,000 semi-mature trees will form the roots of the 100 hectare Olympic park which organisers say will create a "festival atmosphere".
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