The Imbrium Basin is the largest basin on the nearside of the Moon, with a diameter of 1,160 kilometers (the South Pole-Aitken Basin on the farside is twice as large). The Imbrium Basin is also the second youngest basin on the Moon. Based on samples returned by Apollo 15, it formed about 3.85 billion years ago. It was subsequently filled in with volcanic basalt lava seen in this image as the dark areas.
This image - taken by NASA's Lunar Orbiter 4 - provides an overview of the Mare Imbrium region, which occupies the upper left portion of the image. Part of Mare Serenitatis is visible in the upper right. Imbrium and Serenitatis are separated by the Montes Apennine, which form part of the main basin ring of the Imbrium Basin. On the northeast side of Imbrium are the Montes Alpes, which are another part of the main Imbrium Basin ring. The Vallis Alpes cuts through the Montes Alpes near the one o'clock position around the Imbrium Basin. Copernicus Crater is prominent in the central portion of the image, just below Mare Imbrium.
Image Credit: NASA
Credit: Lunar and Planetary Institute