Eighteen acres of Pilot Knob, a cherished tract of Minnesota history that was under threat of townhouse development just a few years ago, will be preserved as open space in a deal completed Thursday.

The nonprofit Trust for Public Land conveyed the land to the city of Mendota Heights, which will manage that tract and 8 1/2 acres purchased two years ago. The land will be returned to its natural state with prairie grass and oak trees for use as a passive-use park, said Bob McGillivray, the TPL's senior project manager.

"I view this as really putting a death knell on development there," he said, describing the importance of the sale in the year of Minnesota's 150th birthday. "This is overlooking the area where our state was born."

Riverboat pilots hauling supplies to nearby Fort Snelling gave Pilot Knob its name. The Mdewakanton and Wakpehkute Dakota tribes named it Oheyawahi, meaning "the hill much visited," and consider the land sacred ground because they buried their dead there. It's also where they signed the Treaty of 1851 that ceded 35 million acres of Dakota land to the U.S. government.

The land secured Thursday was owned by nearby Acacia Memorial Park Cemetery for possible future expansion and cost $1.88 million largely paid in grants, said Brian Madson, a TPL spokesman. Those 18 acres, combined with the previous purchase and a few small tracts of city-owned land, make about 25 acres available for permanent preservation in a natural state, McGillivray said.

A coalition of American Indians, historians, archaeologists, religious groups, local residents and others rallied to save Pilot Knob after private developers proposed building 157 luxury townhomes there.

"It's wonderful to recognize that it's public land for the ages," said Gail Lewellan of Mendota Heights, an organizer of the Pilot Knob Preservation Association. She said that "in a world where so much land is being altered for development," Pilot Knob is now an outdoor classroom where schoolchildren can learn how Minnesota looked hundreds of years ago.

Volunteers are restoring it much as it appears in an 1840s painting by Seth Eastman, she said.

Kevin Giles • 651-298-1554