There simply isn't enough time or space to list every mass shooting in the US in this blog; we don't even have a confirmed record of the mass shootings in this country. The best we have is the National Violent Death Reporting System, which is a state-based program under the CDC and includes only 32 states. And the House recently vetoed a proposed amendment to allow the CDC to research gun deaths.
But we need to start somewhere. If we use the definition of "four or more people are wounded or killed", there have been more mass shootings in the US this year than days passed of 2016. Let me repeat that.