An Amtrak (search) train carrying 103 people derailed in eastern Missouri after apparently striking boulders on the tracks from a rockslide, officials said Thursday. About 20 people sustained minor injuries.

The Texas Eagle, which runs between Chicago and San Antonio, derailed around 11:30 p.m. Wednesday while carrying 90 passengers and 13 crew members. One passenger and one crew member remained hospitalized Thursday, said Amtrak spokesman Marc Magliari.

The train was moving slowly through a winding area near Blackwell (search), about 50 miles southwest of St. Louis, when it struck the rockslide, Jefferson County Sheriff Glenn Boyer said Thursday. He described boulders about half the size of a car hood on the track.

"We're fortunate the engineer had to slow down," Boyer said. "It probably could have been a lot more serious."

Tracks at the derailment site were expected to reopen by Thursday evening, and arrangements were being made to help passengers continue their travels, Magliari said.

The National Transportation Safety Board (search) has decided it will not investigate the derailment, spokesman Terry Williams said.