Investigators said the woman was moving south on Alicia Parkway near Aliso Hills Drive about 7:20 p.m. when the man tried to drag her into some bushes.
"He came up behind me and pushed me so hard that I lost my balance," said the woman, who only wanted to be identified as J. "I was screaming, but the cars were driving so fast no one could hear me."
J said her attacker then pushed her further down the dark ravine out of view of traffic. That's when she started fighting back.
"All I could say was I need to get out of this ravine because if he's fighting me, at least if I'm on the street people can see," she said. "I started screaming the words, 'No, no, no.'"
J said she stepped toward the suspect, he backed up and tripped, and then she took off running.
"A suspect that would do that at 7:20 p.m. on a busy street like this is liable to do anything," said spokesman Jim Amormino of the Orange County Sheriff's Department. "Only her bravery saved her form the sexual attack."
The suspect was described as 5-foot-8 with a stocky build. He has short brown hair with long, curly hair on the sides. He wore dark fitted clothes and tennis shoes.
"I want people to know that it's OK to run, it's OK to go for walks, but be aware there are predators out there every day and the only way to protect yourself is by taking extra steps to fight back," J said.
Anyone with information is asked to call Orange County sheriff's investigators at (866) 847-6273.