This US Supreme Court case involved a dispute between the Dubuque and Sioux City Railroad Company (DSC) and the Des Moines Valley Railroad Company (DMV). DSC had been granted a charter by the state of Iowa to construct a railroad from Dubuque to Sioux City. DMV had been granted a charter to construct a railroad from Des Moines to Sioux City. DSC argued that DMV's charter was in violation of its own charter, as it would be competing with DSC for the same business. The Supreme Court held that DMV's charter was not in violation of DSC's charter. The Court reasoned that the two charters were not in conflict, as the two railroads were not competing for the same business. The Court noted that the two railroads were operating in different parts of the state, and that the two charters were not in conflict. The Court also noted that the two charters were granted by the state of Iowa, and that the state had the authority to grant such charters. The Court concluded that DMV's charter was not in violation of DSC's charter, and that the two railroads were not competing for the same business. The Court held that the two charters were not in conflict, and that the state of Iowa had the authority to grant such charters.

Justice Field delivered the dissenting opinion in Dubuque and Sioux City Railroad Co. v. Des Moines Valley Railroad Co, arguing that the majority had misconstrued the language of a contract between two railroad companies, and thus reached an incorrect conclusion as to which company was entitled to certain land grants from Congress. He argued that while it is true that one party may not be allowed to take advantage of its own mistake or ambiguity in a contract, this does not mean they should be held liable for mistakes made by another party when there is no evidence of fraud or bad faith on their part. In this case, he argued that since both parties were equally mistaken about what was meant by certain terms used in their agreement - such as "the main line" - neither could claim any rights over the other based on those terms alone; rather, each must look at all relevant facts surrounding their agreement before making any determination regarding who has superior rights under it. Ultimately Justice Field concluded that because there was no clear indication either way as to which company had superior rights under the contract's ambiguous language, neither should have been awarded exclusive control over these lands granted by Congress without further investigation into all relevant circumstances surrounding them