 Diaz won the crown and title of Miss Earth United States 2009 on July 22, 2009.She represented the United States in the 9th edition of Miss Earth beauty pageant, which was held at the Boracay Ecovillage Resort and Convention Center, in the Island of Boracay, Philippines, which started on November 1, 2009 and concluded on November 22, 2009.The Miss Earth winner serves as the spokesperson for the Miss Earth Foundation, the United Nations Environment Programme (UNEP) and other environmental organizations.