The alleged victim said the former Radio 1 DJ became "frisky" with her after she was invited into his caravan at the gig on a farm in the late 1970s.
In a videoed police interview played to the court, the woman said she was talking about music with Mr Travis inside the caravan when he offered to sign her poster.
He then "lunged forward", she said.
She added: "He started snogging my face off. He got his hand up my shirt and pulled my bra up.
"He was so heavy I was trapped in the seat. I could not get up. I thought he was going to rape me."
The woman told police Mr Travis then suddenly got up and told her to leave before she hitch-hiked home.
Asked how she felt during the incident, she replied: "Petrified."
Mr Travis, whose real name is David Patrick Griffin, is charged with 13 counts of indecent assault dating back to between 1976 and 2003, and one count of sexual assault in 2008.
The 68-year-old, from Buckinghamshire, is accused of assaulting 11 women, one of whom was 15 at the time. He denies all the charges.
The woman's interview with police was played to London's Southwark Crown Court.
During it, she said: "He put his hand up my skirt, to my thigh. I was crying, I was shouting at him to stop - then he did.
"I don't know whether he had a conscience.
"He stopped and told me I should get dressed. He realised he wasn't going to get anywhere with me."
The witness described herself as naive at the time of the incident.
During cross-examination, Stephen Vullo, defending Mr Travis, said: "I'm going to suggest to you that none of this ever happened. What do you say to that?"
She replied: "I'd say that's untrue because it did."
Giving evidence, former Showaddywaddy lead singer Dave Bartram said "on regular occasions" the band would be introduced on stage by Top Of The Pops presenters and DJs, including Mr Travis.
Asked whether he could remember the concert in Gloucestershire where Travis allegedly assaulted a 15-year-old girl, Mr Bartram replied: "I can actually recall it, simply because Dave came on stage with the band and proceeded to make a nuisance of himself.
"When Dave came on stage, I'm not sure if he was invited or uninvited, he got on one of the drum kits and proceeded to make a bit of a racket."
Mr Bartram, who told the court he appeared on Top Of The Pops more than 50 times, added that Mr Travis had "a great presence".
The court had earlier heard from other women who said that they had been abused by Travis.
A headteacher said she recoiled after being indecently assaulted by the DJ at a student gig in Nottingham at the height of his fame.
The trial continues.