The IOC expelled Moreno from the games, revoked her accreditation and asked cycling's world governing body, the UCI, to follow up for any further sanctions.
Athletes found guilty of using EPO normally face a two-year ban.
Eugenio Bermudez, secretary general of the Spanish cycling federation, said Moreno's 'B' sample also came back positive on Sunday night.
The 27-year-old is the first athlete caught under the IOC's Beijing drug-testing program, which began with the opening of the Olympic village July 27 and runs through the end of the games on Aug. 24.
The program includes a record 4,500 doping controls, with athletes subject to unscheduled tests at any time and any place.
Under a new IOC rule, Moreno will be barred from the 2012 London Olympics if she receives a doping ban of more than six months.
"The IOC means business," Davies said.
Moreno, a three-time Spanish national champion, is not a major name in cycling and was not considered a likely medal contender in Beijing.
She was a third-place finisher at the women's Giro in Italy in 2007.
Moreno had cited an anxiety attack for her decision to return to Spain on the day of the drug test.
Spanish Olympic committee spokesman Jose Maria Bellon said a team doctor had examined Moreno on July 31 and determined she was not fit to compete.
"It's very surprising. It appears that the Spanish anti-doping controls didn't detect anything in their tests back in Spain before the athlete traveled out," Bellon said.
"We don't know how many tests she underwent, but obviously she didn't pass the last one. We're examining the case."
Moreno said on her website that she was "taking advantage of several days to relax and recuperate from the strong anxiety attack suffered" in Beijing.
With Moreno's departure, the Spanish team had two riders instead of three in Sunday's road race, which was won by Britain's Nicole Cooke.
Moreno had also been scheduled to race in Wednesday's time trial.
Spanish cyclists have been under intense scrutiny since Operation Puerto, a blood doping investigation launched in Madrid in May 2006 that has implicated dozens of riders.
Two Spanish cyclists, Moises Duenas Nevado and Manuel Beltran, tested positive for EPO during this year's Tour de France.