Cannot load massive menu

My site contains 20,000 pages that I want to display on the side navbar. FYI, it contains Top level menu, then submenu for US state,then submenu of each city within the state.

I applied the fix for a memory error I got that if found here – http://www.niharsworld.com/2009/08/18/wordpress-fatal-error-allowed-memory-size-xxx-bytes-exhausted-solved-php-error/

Now the page simply fails to load. I am using the GD Pages navigator to manage how the menus expand but the sheer size of the menu seems to be a problem. Any suggestions?