The majority of the 41 county bridges in North Dakota that have been closed after inspections the past two years are in the eastern part of the state, and officials say that is no coincidence.

That part of the state has more rain and flatter terrain, leading to more drainage ditches and ravines, state Transportation Director Francis Ziegler said. Section lines, which divide tracts of rural property, also tend to be more developed in eastern North Dakota, he said.

"Whenever you hit a ravine or whatever, you need to cross it," Ziegler said. In many cases, he said, the preferred method in the past was a timber bridge, and those bridges deteriorate over time.

The Transportation Department recently finished a bridge inspection project that Gov. John Hoeven ordered in late August after the Interstate 35W bridge collapse in Minneapolis that killed 13 people and injured dozens.

Officials inspected 751 North Dakota bridges deemed structurally deficient. Most of them were county bridges.

Nineteen low-traffic county bridges were closed - along with a steel-and-concrete bridge on U.S. Highway 281 in the Devils Lake region that Ziegler said will be repaired and reopened within a few weeks.

Inspectors also noted that 22 county bridges were already closed as a result of the state's regular inspection process, in which each of the 5,026 bridges in the state are examined once every two years.

Of the 41 county bridges shut down in North Dakota, 32 are in the eastern part of the state.

"It's the topography," Ziegler said. "If you think of the Red River Valley, it's very flat. Everything ultimately is drained by ditches."

Bradley Rundquist, an associate professor of geography at the University of North Dakota, said the Red River Valley is "one of the flattest places on the planet" and that people who want to move water off land have little choice but to use drainage ditches.

"I would expect just through sheer numbers, the fact that you have more drainage ditches, you need more bridges," he said.

County officials will decide the fate of the county bridges that have been closed. Counties that decide to replace a bridge can apply for some of the $9 million the state receives each year in bridge replacement money from the federal government.

North Dakota and Minnesota officials also recently finished inspecting 36 bridges over the Red River, which forms the border between the two states. In late August, a bridge over the river near Drayton in Pembina County was closed for about four days so officials could repair a crack under its deck.

A bridge over the river in Traill County was closed earlier this month because of shifting soil that exposed timber pilings. A new bridge is to be built, starting in 2008, the Transportation Department said.