The Challenger Deep is a relatively small slot-shaped depression in the bottom of a considerably larger crescent-shaped oceanic trench, which itself is an unusually deep feature in the ocean floor. The Challenger Deep consists of three basins, each 6 to 10 km (3.7 to 6.2 mi) long, 2 km (1.2 mi) wide, and over 10,850 m (35,597 ft) in depth, oriented in echelon from west to east, separated by mounds between the basins 200 to 300 m (656 to 984 ft) higher. The three basins feature extends about 48 km (30 mi) west to east if measured at the 10,650 m (34,941 ft) isobath.[10] Both the western and eastern basins have recorded depths (by sonar bathymetry) in excess of 10,920 m (35,827 ft), while the center basin is slightly shallower.[11] The closest land to the Challenger Deep is Fais Island (one of the outer islands of Yap), 287 km (178 mi) southwest, and Guam, 304 km (189 mi) to the northeast.[12] Detailed sonar mapping of the western, center and eastern basins in June 2020 by the DSSV Pressure Drop combined with crewed descents revealed that they undulate with slopes and piles of rocks above a bed of primordial ooze.