BAKER CITY — Baker City and Baker Valley residents might see a strange-looking helicopter flying low later in May.

The aircraft will have something resembling an insect’s proboscis jutting ahead of and beneath its nose as it flies a precise grid pattern across the valley.

The chopper won’t be spraying anything, said Jason McClaughry, geological survey and services program manager at the Oregon Department of Geology and Mineral Industries field office in Baker City.

As his title suggests, the purpose of these flights, which could start late this week or early next week and continue for three or four days, has to do with geology.

Specifically, the sensor mounted on the helicopter’s boom will measure minuscule variations in the Earth’s magnetic field.

The magnetometer takes a measurement 10 times per second, and a GPS system pegs the sensor’s position to within an accuracy of 2 to 4 feet.

Computers will then

assemble this massive amount

of data into high-resolution maps that give geologists information about rock formations, including earthquake faults, that, because they’re underground, can’t otherwise be detected, McClaughry

said.

Different types of rocks have different, but predictable, effects on the magnetic field, he said.

The aerial survey, and the ability to “see” underground is especially valuable in Baker Valley, he said, where there are relatively few rock outcroppings that geologists can study.

“So much of the geology is

buried by sedimentary fill,” he

said. “We can map the fringes but we don’t know as much about the valley.”

Ice Age glaciers that mantled

the Elkhorn Mountains and

flowed through canyons on the

east slopes, such as Rock Creek

and Dutch Flat Creek, deposited piles of rock and gravel, McClaughry said.

Streams have done the same, leaving “alluvial fans” that covered the bedrock.

This murky geologic picture makes it harder for geologists to map and study earthquake faults, McClaughry said.

The much more detailed maps possible with the new data from the helicopter-mounted sensor — known as “aeromagnetic surveys” — will help geologists make better estimates of the earthquake risk in and around the valley, he said.

Where’s the water?

But understanding local earthquake danger isn’t the only benefit of the upcoming surveys and the maps they make possible.

McClaughry said the new maps, by showing faults and other fissures and gaps in the bedrock, will allow geologists to get a sense of how groundwater moves through the valley.

That information can potentially help officials and landowners use water more efficiently, according to the state geology department.

The new maps will also show minerals that could be used for “modern technologies, economies and natural security,” according to the geology department.

The mineral data will come from another sensor attached to the helicopter, McClaughry said.

That sensor will estimate the

concentrations of radioactive elements potassium, uranium and thorium in the rocks by measuring the natural gamma radiation those rocks emit.

This “radiometric” survey can

be done simultaneously with

the measuring of variations in

the magnetic field, McClaughry said.

He said geologists will compare the radiometric survey results with lab tests of rock samples collected on the ground to further refine geologic maps.

Data lacking in Baker Valley

McClaughry said the U.S.

Geological Survey has done aerial surveys to produce detailed maps for other parts of Northeastern

Oregon, including the Pendleton area and the Grande Ronde

Valley.

But the survey areas haven’t extended south of Ladd Canyon.

The geology department will also be doing aerial surveys in the Burns area and near Dixie Butte, northeast of Prairie City, this month and in June.

The state is working with NV5, an engineering firm that has an office in Corvallis, and a Colorado firm, EDCON-PRJ, on the mapping project.

Precision GeoSurveys, of British Columbia, will oversee the helicopter flights.

The helicopter will fly about 400 feet above the ground in most areas, except 500 feet while over Baker City to reduce rotor noise, according to the geology department.

The aircraft will fly a grid

pattern with the east-west lines

650 feet apart, and the north-sound lines 1.2 miles apart, McClaughry said.

The sensors are passive, meaning they don’t emit energy, according to the geology department.

The helicopter will have an altimeter that uses an “eye-safe infrared laser to monitor flying height above the ground.”

The helicopter will not take any photographs or video images during the surveys, according to the geology department.