LONDON -- It was a quick and disappointing exit from the London Games for two-time Olympian Jill Camarena-Williams,

The 30-year-old Stanford grad, slowed by a back injury, bowed out in the Monday morning prelims of the women's shot put, throwing just 59 feet, 9 1/2 inches.

"I hurt myself this last week, and I haven't been able to practice pretty much the whole time I've been in England," she said. "It's been a rough go, but I just wanted to go out and try my hardest, and that is what I did."

Camarena expected to improve on her 12th-place finish in Beijing four years after after a breakthrough summer in 2011. She became the first American to claim a medal in the event at the IAAF world championships, finishing third in Daegu, South Korea, and tied the 23-year-old U.S. record with a throw of 66-2 1/2.

Camarena has a history of back problems, but remained healthy in recent years, in part due to the assistance of husband and trainer Dustin Williams. She withdrew from a meet in Europe just before the Olympics because her back flared up, but Dustin Williams later said in an email to this newspaper she was feeling better.

In London, Camarena was attempting to become the first American on the women's shot put medal podium since Earlene Brown won bronze in 1960.

American Michelle Carter, daughter of former 49ers star Michael Carter, threw 59-9 1/4 to advance to Monday night's final.

The top qualifiers, as expccted, were Nadzeya Ostapchuk (68-1 1/2) of Belarus and Valerie Adams (66-11 1/4) of New Zealand.