Query: Cordilleran Ice Sheet is made up mostly of snow.

Relevant passages:
Ice sheet <=SEP=> An ice sheet is a mass of glacier ice that covers surrounding terrain and is greater than 50000 km2 , thus also known as continental glacier . The only current ice sheets are in Antarctica and Greenland ; during the last glacial period at Last Glacial Maximum ( LGM ) the Laurentide ice sheet covered much of North America , the Weichselian ice sheet covered northern Europe and the Patagonian Ice Sheet covered southern South America .   Ice sheets are bigger than ice shelves or alpine glaciers . Masses of ice covering less than 50,000 km2 are termed an ice cap . An ice cap will typically feed a series of glaciers around its periphery .   Although the surface is cold , the base of an ice sheet is generally warmer due to geothermal heat . In places , melting occurs and the melt-water lubricates the ice sheet so that it flows more rapidly . This process produces fast-flowing channels in the ice sheet -- these are ice streams .   The present-day polar ice sheets are relatively young in geological terms . The Antarctic Ice Sheet first formed as a small ice cap ( maybe several ) in the early Oligocene , but retreating and advancing many times until the Pliocene , when it came to occupy almost all of Antarctica . The Greenland ice sheet did not develop at all until the late Pliocene , but apparently developed very rapidly with the first continental glaciation . This had the unusual effect of allowing fossils of plants that once grew on present-day Greenland to be much better preserved than with the slowly forming Antarctic ice sheet .

Cordilleran Ice Sheet <=SEP=> The Cordilleran ice sheet was a major ice sheet that periodically covered large parts of North America during glacial periods over the last ~ 2.6 million years . This included the following areas :   Western Montana  The Idaho Panhandle  Northern Washington state down to about Olympia and Spokane  All of British Columbia  The southwestern third or so of Yukon Territory  All of the Alaska Panhandle  South Central Alaska  The Alaska Peninsula  Almost all of the continental shelf north of the Strait of Juan de Fuca   The ice sheet covered up to 2.5 million square kilometres at the Last Glacial Maximum and probably more than that in some previous periods , when it may have extended into the northeast extremity of Oregon and the Salmon River Mountains in Idaho . It is probable , though , that its northern margin also migrated south due to the influence of starvation caused by very low levels of precipitation .   At its eastern end the Cordilleran ice sheet merged with the Laurentide ice sheet at the Continental Divide , forming an area of ice that contained one and a half times as much water as the Antarctic ice sheet does today . At its western end it is believed nowadays that several small glacial refugia existed during the last glacial maximum below present sea level in the now-submerged Hecate Strait and on the Brooks Peninsula in northern Vancouver Island . However , evidence of ice-free refugia above present sea level north of the Olympic Peninsula has been refuted by genetic and geological studies since the middle 1990s . The ice sheet faded north of the Alaska Range because the climate was too dry to form glaciers .   Unlike the Laurentide ice sheet , which is believed to have taken as much as eleven thousand years to fully melt , it is believed the Cordilleran ice sheet , except for areas that remain glaciated today , melted very quickly , probably in four thousand years or less . This rapid melting caused such floods as the overflow of Lake Missoula and shaped the topography of the extremely fertile Inland Empire of Eastern Washington .