The 32-hectare artwork, which was done last week and reads "Heartland#NoKXL," is the latest protest environmentalists and landowners have employed against TransCanada's proposed Keystone XL pipeline.
Critics of the pipeline want President Barack Obama to reject the project because they fear it could contaminate groundwater and contribute to pollution.
TransCanada (TSX:TRP) has said the pipeline will have upgraded safety measures, including remote control shut-off valves and frequent inspections. It has already built the southern leg of the pipeline between Oklahoma and Texas.
The section of the project that still needs approval would cross Montana, South Dakota, Nebraska and Kansas.
More than five years have passed since TransCanada first proposed the project to complement its existing Keystone pipeline.
Last week, 11 Senate Democrats urged Obama to approve the project by the end of May, so that another construction season won't be lost.
The U.S. State Department and the president have authority over the project because it crosses a U.S. border.
TransCanada also has proposed connecting it to the Bakken oil field in Montana and North Dakota.
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