USPS -- Wild and Scenic Rivers stamp sheetlet
In 2018, the National Wild and Scenic Rivers system celebrated its 50th birthday, as it was founded in 1968. USPS made a sheetlet commemorating the NWSR's 50th birthday. They released a sheet of 12 stamps depicting different WSRs. In the background is the Merced River of California. It shows (on row 1) the Merced River, the Owyhee River, the Koyakuk River, (on row 2) the Niobrara River, Snake River, the Flathead River, (on row 3) the Missouri River, Skagit River, the Deschutes River, (on row 4) the Tlikakila River, Ontonagon River, and the Clarion River. It's still commonly confused with the National Parks and Monuments, etc. The sheetlet was released on May 21, 2019 in Bend, Oregon.