A few months ago, I put together a chart showing the various mergers and splits among Reformed denominations in the US. My chart shows both Presbyterian and Reformed denominations and is, I hope, a cleaner version than some other charts out there. Below are links to PDF, PNG, and SVG versions. Please feel free to leave feedback in the comments. I hope the chart is useful to you!
Also, I would love to include the various Korean Presbyterian denominations that exist in the United States, but have no sources for information about them. If anyone would like to point me to sources, I will add them to the chart.