It is named for the American geologist Alfred Hulse Brooks, who first delineated the range’s geologic character.
Except for the east-flowing upper portion of the Colville River, most drainage is northward.
The tundra-covered area, called the , is underlain by permafrost, which is permanently frozen sediment and rock; only a shallow surface zone thaws during the short summer, producing a vast number of small ephemeral lakes and ponds.
There are enormous calderas—collapsed craters marking past volcanic eruptions.
In 1912 one of the most-spectacular of recent historic eruptions occurred when a volcano in the Aleutian Range erupted and formed the and Mount Spurr and extends in a great arc some 600 miles (1,000 km) to the Canadian border at the southeastern end.
The bedrock includes tightly folded Paleozoic and Mesozoic sediments and volcanics and (i.e., formed in the past 66 million years) intrusions.