Construction of a four-lane St. Croix bridge shifts this week from maps and blueprints to roaring motors and a changing landscape in Oak Park Heights, the new host city.

An influx of heavy equipment means that work on the new bridge and its approach highways has begun in earnest. The work signals an impending retirement for the 1931 Stillwater Lift Bridge, about 2 miles to the north, which in 2017 will be closed to vehicle traffic and become part of a pedestrian loop trail.

The St. Croix Crossing project includes a roadway approach on the Wisconsin side of the river, historic and environmental mitigation, and trails for walking and cycling. Dozens of contractors and thousands of workers will be involved at the peak of the construction.

"I think that the communities will have an iconic bridge they will be pleased with that will serve them for years to come," said Mary McFarland Brooks, a spokeswoman for the Minnesota Department of Transportation (MnDOT). "I think it will be something that people will be proud of."

Here's the latest in the two-state project, estimated to cost as much as $690 million:

• Preparation begins for reconstruction of Hwy. 36 and Hwy. 95. Work involves clearing trees and vegetation as well as removing pavement from the "Village Neighborhood" area in Oak Park Heights off Beach Road.

Work will continue for about two weeks in the area, where houses were removed in the 1990s. Roads into the work area will be barricaded. A popular traffic shortcut, 59th Street between Hwy. 95 and Stagecoach Trail, will permanently close.

Two trees with eagles' nests will be preserved in the construction zone, McFarland Brooks said. "The eagles remain in their home," she said last week.

• Crews are building a construction staging area on the Minnesota side of the St. Croix River for the bridge foundations. A new dock wall will support equipment and material. Cranes and barges are being hauled to the site.

• MnDOT and its companion agency in Wisconsin will hold several public open houses to acquaint residents with the bridge project and how it affects them.

Minnesota open houses are scheduled for: May 21, 4:30-6:30 p.m., Oak Park Heights City Hall, 14168 Oak Park Blvd. N.; May 30, 4:30-6:30 p.m., Bayport Public Library, 582 4th St. N.; June 11, 4:30-6:30 p.m., Stillwater Public Library, 224 3rd St. N.

Wisconsin open houses are scheduled for: May 23, 5-7 p.m., Hudson High School Cafeteria, 1501 Vine St.; June 4, 6:30-8 p.m., Houlton Elementary School, 70 County Hwy. E.

• Boaters can expect a channel "narrowing" and a no-wake zone beginning in late May near Sunnyside Marina. The restriction will result from work on bridge footings in the river.

• MnDOT will do public programming on Valley Cable in June to inform Washington County residents about the latest work.

• A groundbreaking for the bridge project will be held May 28 at 2:30 p.m. at Lowell Park in Stillwater. Govs. Mark Dayton of Minnesota and Scott Walker of Wisconsin are expected to attend.

• Restoration of the Lake St. Croix Overlook in Oak Park Heights has begun. Improvements will include replacing portions of the rock wall, repaving the area, replacing and updating interpretive history, and restoring landscaping to its native state.

The overlook was one of a series of "highway rests" built by the National Youth Administration, a federal poverty-relief program, in the late 1930s.

• MnDOT is writing a curriculum that schools can use to teach students about the work behind the bridge project.

The S.T.E.M. (science, technology, engineering and math) program will make engineers and materials available to classes and already involves schools in Stillwater and Somerset, Hudson, New Richmond and Houlton in western Wisconsin.

Schools wanting to participate can contact McFarland Brooks at 651-366-4280.

• A new parking lot will be built east of Club Tara, a longtime restaurant south of Hwy. 36 in Oak Park Heights.

• MnDOT is working with the Washington County Sheriff's Office on a Code Red capability that would enable e-mail alerts to specific residents affected by construction.

• Protected mussel populations have been found on the Wisconsin side of the bridge project and no work will occur there until conservationists from both states are able to move them, McFarland Brooks said. These are different from zebra mussels, an invasive species that temporarily halted barge work recently.

Work begins soon on rebuilding frontage roads along Hwy. 36 through Oak Park Heights. Later stages will include reconstructing and realigning Hwy. 36 and rebuilding intersections at Oakgreen-Greeley and Osgood Avenues.

• On the Wisconsin side of the river, some landowners whose property lies in the path of highway construction have received purchase offers. More offers will be mailed this month, WisDOT spokeswoman Chris Ouellette said.

Owners have 60 days to seek their own appraisal if they choose. If an agreement can't be reached, WisDOT will begin eminent domain proceedings, Ouellette said.

WisDOT plans to acquire all needed property by this fall for the first portion of the highway project, which will extend about 1 mile from the bridge site to County Road E near Houlton School, where a diamond interchange will be built.

The second project will extend the highway about 2 miles from County Road E north to Hwy. 64.

• Endangered dotted blazing star flowers were moved from the path of the highway last fall, but WisDOT will check the area again this spring to make sure none remains. The dotted blazing stars are being nurtured in nurseries for transplanting this spring and summer.