The origin or the monel-metal rivets is somewhat of a mystery to define what agency actually placed them. Many are found along railroads, so they could have been placed by railroad surveyors in structures such as signal bases and concrete culvert headwalls. When USC&GS ran their level lines along many of the C&NW Railroad lines in Nebraska, they utilized many of these rivets and assigned numbers to them. The rivets also appear in areas where the State Surveys of the Great Depression occurred away from railroads, so it is possible that this agency might have been using them also.
The word "monel" refers to an acid-resisting alloy of approximately 65% nickel and 35% copper. Also traces of iron, manganese, carbon, and silicon are used in their manufacture. They are stainless steel in appearance which a shiny surface. The head of the rivet is about 1/2" to 5/8" in diameter and rounded on top. The rivet that was assigned as No. 1, "RV 1", was at O'Neill, Nebraska.
This rivets can be located with a surveyor grade magnetic locator such as the Schoenstedt brand.