Laurie, you made a keen observation. It is an inkwell but it doesn't commemorate the discovery of gold.
Steve, it's not about the Trans-Pacific Cable.
Gene, yes this beautiful piece was presented to Abraham Lincoln. The helmet you see is not a soldier's helmet. To clarify, yes, the Transcontinental Railroad was completed in 1869 however it didn't cross this territory. Work here to connect to it didn't begin until 1878.
Hint # 4 This piece is tied to a bill passed by Congress in 1863 and signed by Lincoln.