A 20-year-old woman was seriously injured early Thursday morning when she fell from the fifth-story window of the Spanish Towers apartments, in the 800 block of 29th Street, according to Boulder police.

Boulder police spokeswoman Sarah Huntley said the woman, whose name was not released because police are still investigating the incident, "sustained serious bodily injury but is expected to recover."

The woman, who had traveled to Colorado from California to visit her older sister, had consumed "a couple of tequila shots, at least two lemonade vodka drinks and probably a couple of beers" at a rooftop party at the Spanish Towers, Huntley said.

She said the older sister told police she "believed her sister was not heavily intoxicated."

The older sister, who is a student at the University of Colorado, told police she put her little sister to bed around 1:10 a.m. and checked on her twice over the next hour, Huntley said.

The second time she checked on her sister -- around 2:05 a.m. -- she had gone missing, Huntley said. An ambulance was already pulling up to the east side of the south tower on reports of a woman lying in the grass with a window screen near her, Huntley said.

She said the bed the woman was sleeping in was right next to the window.

"It's not clear if she rolled out of the window, crawled out of the window or what transpired," Huntley said.

She said the woman underwent surgery Thursday and is recovering. She did not provide the victim's specific condition.