The incident occurred at about 1:30 p.m. on Stevens Creek Trail, Mountain View police spokeswoman Liz Wylie said.
The woman was jogging on the trail near the Dana Street overcrossing when an overweight man in a red hooded sweatshirt blocked her path, Wylie said.
The man picked her up in a bear hug and carried her toward some bushes along the creek, but she began scratching his face and was able to fight him until he dropped her, Wylie said.
The man fled south on a green mountain bike and the woman, who was uninjured, borrowed someone's cell phone to call 911, Wylie said.
The man is described as white, about 35 years old, with dark, thinning hair and a full goatee.
Police are investigating the case as an attempted sexual assault and, although they have not received reports of any similar crimes on Stevens Creek Trail, are urging residents to report any suspicious activity in the area.