By Kevin Murphy

(Reuters) - A Colorado woman police believe faked a pregnancy was charged on Friday with the kidnapping in Wisconsin of her 6-day-old nephew, who was found a day later behind a gas station in Iowa, federal prosecutors said.

Kristen Smith, 31, of Denver, was charged in a Wisconsin federal court after the infant, Kayden Powell, was found wrapped in blankets in a tote bag 200 miles away from his home, authorities said.

According to the criminal complaint, authorities believe Smith faked being pregnant after they found a prosthetic pregnancy belly in her car and Facebook postings in which she claimed to be with child.

The parents, Brianna Marshall, 18, and Bruce Powell, 23, reported the baby boy missing from his bassinet early Thursday morning, sparking a massive search that rallied federal, state and local officials.

According to the complaint, Marshall told authorities that Smith was at her home until sometime early Thursday morning, when she planned to head back to Denver, where she lives.

Authorities found Smith at a gas station in West Branch, Iowa, where they searched her car and found baby clothing, a car seat and a stroller, but no baby, the complaint said.

The complaint said authorities also found a prosthetic pregnancy belly in her vehicle.

After Smith was arrested because of an outstanding warrant in Texas, authorities examined her cell phone, where they found emails and Facebook postings in which she said she gave birth on Wednesday.

"Smith did not appear pregnant, had not appeared pregnant while in Wisconsin and was pregnancy tested and was not pregnant," the complaint said.

At 10 a.m. on Friday morning, West Branch police found the baby in a tote bag outside another gas station, about 500 yards from where they apprehended Smith, the complaint said.

"Despite frigid temperatures, Kayden was found alive and appears to be doing very well," Kopp told a news conference. "In the words of EMS officials, he is in excellent health."

West Branch is in eastern Iowa about 185 miles from Beloit in southern Wisconsin, near the Illinois border.

(Reporting by Kevin Murphy in Kansas City, Brendan O'Brien in Milwaukee; Writing by David Bailey; Editing by Gunna Dickson and Andre Grenon)