Are you aware that Red Rock, Iowa, no longer exists? It's at least 30 feet below water. In the late 1960s the state of Iowa bought out that area, dammed up the Des Moines River, and created Red Rock Lake, a state park. I don't know if they moved the cemeteries and the headstones before they flooded it.

Unfortunately, you will never find a death certificate for James Brown simply because most states (including Iowa) did not begin to issue birth certificates and death certicates until the 1880s (nearly 20 years after the Civil War). You probably will not find an obituary either because I doubt that a single newspaper existed in this area of Iowa in 1850's. (My family lived in Marion County, too, in the 1860s.) Marion County had just opened for settlement after the U.S. government made a treaty with the Indians around 1848. At the time James Brown died in Marion County, the area would have contained just a few scattered farms. The nearest "big city" would have been Knoxville, Iowa, which contained probably fewer than 10 log cabins.