Highlights of progress at Ground Zero site

There's a whole lot of building going on at Ground Zero.

Work continues on turning the bare concrete plaza into a memorial park, expected to open Sept. 11, 2011.

Tree plantings began Saturday. Both memorial pools are now being clad in granite, and steel erection for the memorial pavilion building is under way. The pools, also set to open next year, occupy the footprints of the Twin Towers.

On Friday, workers were performing the final concrete installation on the site's subgrade structure, including the surrounding plaza.

One World Trade Center, scheduled to be completed in 2013, is rising into the sky. As of Friday, steel was going up on Floor 36 and concrete was being installed on floors 29 and 30. The tower, formerly called the Freedom Tower, will rise 1,776 feet from the ground once completed.

At Towers 2 and 3, drilling, demolition, rock excavation and removal of material are ongoing.

At Tower 4, workers are erecting steel and placing concrete.

At the WTC Transportation Hub, Port Authority crews are performing foundation work and steel installation.