Of course, it all depends on your starting point, but both Antarctica and the United States have plateaus much higher than 600 feet.
Some Plateaus listed on the Merriam-Webster Online Dictionary -
Canadian Shield/Laurentian Plateau
Coconino Plateau
Colorado Plateau
Columbia Plateau
Comberland Plateau
Kaibab Plateau
Kimberly Plateau
THE COLORADO PLATEAU REGION From Bowns Point, at the southeastern rim of the 11,000-foot-high Aquarius Plateau, you can see out over the landscape of southern Utah with the perspective of an Olympian god. In every direction the land falls away in thousand-foot leaps, dropping a vertical mile before finally losing itself in a chaos of mesas, buttes, cliff-walls, terraces, domes, amphitheaters, hogbacks, and canyons. Gigantic landforms rise off that desert floor. To the south, a cliff-wall 2,000 feet high and 50 miles long -- the northern edge of the Kaiparowits Plateau -- points like a semaphore at 10,000-foot-high Navajo Mountain. To the east, the purple domes of the Henry Mountains hover above the mesas and badlands which surround them. A 1,000-foot-high hogback called the Waterpocket Fold shoots across the field of view from south to north, its jagged crestline running straight as an arrow for nearly 100 miles. Forty miles away to the northeast, you can see the 35-mile-wide dome called the San Rafael Swell. Closer at hand lies a 100,000-acre amphitheater ringed by the thousand-foot-high Circle Cliffs. Still closer, to the south and southeast, lies the labyrinthine canyon system of the Escalante River.
The Colorado Plateau is a physiographic "province," a region distinct from other parts of the West. Originally named the "Colorado Plateaus" by explorer John Wesley Powell, the "Plateau" is in fact a huge basin ringed by highlands and filled with plateaus. Sprawling across southeastern Utah, northern Arizona, northwestern New Mexico, and western Colorado, the Colorado Plateau province covers a land area of 130,000 square miles. Of America's 50 states, only Alaska, Texas, California, and Montana are larger.
Geologically, the Colorado Plateau is perhaps best defined by what did not happen to it. While the Rocky Mountains to the east and the basin and range country to the west were being thrust, stretched, and fractured into existence, the Colorado Plateau remained structurally intact.
Mike, the US alone has entire cities located at or above one mile above sea level. Obviously, reading about the Colorado Plateau shows that a 600' altitude is uncommon because of its lack of altitude rather than its height. Further, I have no idea if the Colorado Plateau is the highest Plateau in the world. If I had to bet, I'd bet on either Antarctica or some plateau areound the Himalayas. The Lybian Desert, inside the Sahara, is 1,100,000 square kilometers, almost the same size of the Indian subcontinent, and the Jilf al Kabir Plateau in the Lybian has an altitude of about 2,000 meters. Africa's physical geography is a uniform central plateau comprising a southern tableland with a mean altitude of 1,070 m/3,000 ft that falls northwards to a lower elevated plain with a mean altitude of 400 m/1,300 ft. Although there are no great alpine regions or extensive coastal plains, Africa has a mean altitude of 610 m/2,000 ft, two times greater than Europe.
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