Beginning at the southwest corner of township one hundred forty-one north, range eighty-seven west of the fifth principal meridian, a point on the tenth standard parallel; thence east along the tenth standard parallel to the main channel of the Missouri River; thence in a northwesterly direction along the main channel of the Missouri River to the point where the line between ranges eighty-three and eighty-four west intersects the main channel of the Missouri River; thence south along the line between ranges eighty-three and eighty-four west to the line between townships one hundred forty-three and one hundred forty-four north; thence west along the line between townships one hundred forty-three and one hundred forty-four north to the northwest corner of township one hundred forty-three north, range eighty-seven west; thence south along the line between ranges eighty-seven and eighty-eight west to the point of beginning.