Description from the 2010 festival website:

The USGS Menlo Park Science Center will celebrate Earth Science Day on Thursday, April 22, 2010, from 9:00a – 2:30p, coinciding with the 40th Anniversary of Earth Day. Invitations were sent out to over 400 Bay Area educators, and nearly 1,000 school children in grades 2-6 have signed up to attend. USGS is pleased to host this event that gives students and teachers the opportunity to talk with scientists and learn about the Earth through interactive displays and presentations. Activities and exhibits will be suitable for elementary and middle school students grades (2-6).

Head over to the website for a full description of the exhibits.