The fair drew 1,800 girls from around the Southland in its second year, said Carol Dedrich, spokeswoman for the Scouts. That is up from 1,100 participants in 2009.
"The biggest thing about today is we are creating a forum for learning about science, technology, engineering and math," Dedrich said.
A quad in the middle of the Caltech campus was teeming with girls who talked to female aircraft pilots and engineers affiliated with Caltech and the Jet Propulsion Laboratory. They watched robots at work, learned about DNA and drank solar-powered smoothies.
Two dozen girls came from troops in Burbank, Glendale, La Crescenta and La Cañada Flintridge. In several booths, Scouts in their teens showed younger girls some of the marvels of science.
Glendale-Burbank Troop 5186 ran a booth using natural dyes on muslin fabric, illustrating how well the environmentally friendly dye compared to the synthetic colors on most clothes.
Gabby Carriero of Glendale and Jordan Johnson of Burbank, both 14, explained how troop members used mustard, grapes, coffee and beets as foundation for the dyes, all of which also contain vinegar.
An adult troop supervisor made an observation about the experiment that only a grown-up could make.
"Wine stains more than grape juice," Pam Sorem said.
A short distance away, girls form La Crescenta Troop 772 showed how to conduct electricity with nothing more than a nail, a penny and a lemon.
The members of Troop 7191 learned about water conservation and composting, both important for their Gold Award project on the production and consumption of food.
Chandler Dewey of Glendale said the composting demonstration made her focus on the way products are packaged and the damage they can do.
"It makes you want to watch your every move, and watch what you are throwing away," she said.