The habitat of the Columbian ground squirrel is varied but is usually more humid than that of the Townsend and Washington ground squirrels. The most arid of the lands occupied by them in Washington are the grasslands and wheat fields of the Poulouse country and the eastern border of the state. In northeastern Washington they live in meadows and grasslands in the valleys, in openings in the coniferous forest at higher altitudes and in parks and alpine meadows almost to timber-line on the mountains. Some individuals were in brushy places or even in forests, far from grassy clearings. Near Republic, Ferry County, a Columbian ground squirrel was killed as it ran along a log in dense larch woods. Its burrows were found in a tangle of brush and fallen logs. No clearings, meadow or grassland existed nearby. Narrow bands of cleared land beside roads and railroad tracks are extensively used by these squirrels. Where small meadows or pastures occur, this species lives in dense colonies. If grasslands are extensive it lives in loose colonies, often with considerable distances between individual burrow systems. In the mountains the squirrels are scattered or live in small groups. Burrows of the Columbian ground squirrel are often constructed in the open. Mouths of burrows, especially if the animals are living in colonies, usually are marked by a large pile of excavated earth. If, however, there is some large object on the surface of the ground, such as a stone, stump, or log, the entrance to the burrow is located beside this. Such objects are often undermined and made to settle, eventually becoming buried. The squirrels live under houses, and the yards of abandoned ranch buildings are often infested with them. The burrows of the Columbian ground squirrel have been described by Shaw (1919, 1924B, 1925, A, B, E, 1926) and Bailey (1918: 47). Two types of burrows are constructed, summer burrows and hibernation dens. Summer burrows are used year after year, perhaps by succeeding generations of squirrels. They vary considerably but usually are 3 or 4 inches in diameter and possess several entrances. The depth to which the burrow descends, as well as the number of forks and subsidiary burrows, depends to some extent on the whims of the individual squirrel and the length of time the burrow has been occupied. Usually the burrow reaches a depth of four feet and two or more branches are present. A turning-about chamber is present, not far from the entrance. Here a startled squirrel can turn about and watch the entrance and, if the alarm was false, the squirrel resumes its activities above ground. Nests are above the level of the main burrow system and thus are protected from flooding by rain or melting snow. Stored food and excrement are deposited in separate compartments. Escape entrances, concealed in grass and weeds, for use in case the burrow is invaded, are dug from beneath the surface of the ground and thus are unmarked by any telltale mound of earth.