Great Blue Hole
The Great Blue Hole is a giant marine sinkhole off the coast of Belize. It lies near the center of Lighthouse Reef, a small atoll from the mainland and Belize City. The hole is circular in shape, across and deep. It was formed during several episodes of quaternary glaciation when sea levels were much lower. Analysis of stalactites found in the Great Blue Hole shows that formation took place 153,000; 66,000; 60,000; and 15,000 years ago. As the ocean began to rise again, the cave was flooded. The Great Blue Hole is a part of the larger Belize Barrier Reef Reserve System, a World Heritage Site of the United Nations Educational, Scientific and Cultural Organization (UNESCO).
Blue Mountains (ecoregion)
This ecoregion extends from the Redmond area of Central Oregon, across a wide swath of the Columbia Plateau in Eastern Oregon, to Hells Canyon on the Snake River at the border of the three states. The ecoregion is named for the Blue Mountains and contains a complex of basins and mountain ranges that, at average 2100-2900m, are lower and more open than the neighboring Cascades and Northern Rocky Mountains but do include some steep landscape of which Hells Canyon at 1,660m is North America's deepest gorge. The mountains of the ecoregion include the Strawberry Range, Greenhorn, Elkhorn, Aldrich and Maury Mountains in the Blue Mountains, the gentler Ochoco Mountains to the west and the rugged Wallowa Mountains to the east. Rivers include the Grande Ronde, Powder Rivers and Malheur Rivers, all tributaries of the Snake and the John Day and Umatilla Rivers, tributaries of the Columbia.