One of the most common animals in the State is Richardson's ground squirrel, otherwise known as the gopher or "flickertail." It is from this tiny, agile, yellow creature that North Dakota gets its name of "the Flickertail State." Another familiar prairie animal is the jack rabbit. Fish life, like that of plants and animals, has been adversely affected by recent droughts, but efforts are being made to propagate fish and to provide sufficient water for their existence. In the larger lakes and rivers, perch, black and rock bass, pickerel, pike, sunfish, and catfish are found. Some landlocked salmon have been introduced, but they are not adapted to North Dakota lakes and streams. Suckers and carp are common but they are not considered desirable game fish. INDIANS AND THEIR PREDECESSORS PREHISTORIC MAN IN NORTH DAKOTA Just when and where in the shadowy, endless past the Indians of North Dakota, or even of the two Americas, began to break away from the parent stem is not known. Weapons and tools shaped from stone and found in strata that settled into place near the end of the Pleistocene, or glacial, period indicate that as much as 15,000 to 20,000 years ago men wandered along the rivers and through the swamps of those areas that later became New Mexico, Nebraska, and Minnesota. Very probably, in long hunts after game, parties of these men penetrated what is now North Dakota. Stone tools and weapons found in the vicinity of Bismarck suggest an early occupation of the area, how long ago no one knows. A great many years nearer the present day, but still possibly a thousand or more years ago, men were digging busily in the flint quarries 19 miles north of Hebron and 12 miles northwest of Dodge and at other points on the Knife River. With the flint obtained here they fashioned arrowheads and spear points to kill buffalo or to protect their homes against enemy tribesmen. One of these heavily sodded sites on the Knife River contains more than 300 pits, most of which are from 8 to 10 feet across, and from 3 to 5 feet deep. The extensive mounds and earthworks found in the eastern half of North Dakota have been only imperfectly investigated so far, partly because archeologists have but recently recognized the possibilities of the area. The skeletons and the bone and stone manufactured articles lately discovered, however, as well as the general finds of the region, suggest the probability of outlining tribal movements of importance. There is an increasing suggestion that before the time of the historic tribes the prairies of the eastern half of the State supported large populations. It is thought that, just as the Cheyenne are known to have done in the historic period, in prehistoric time the Assiniboin and the Blackfeet, and preceding them still other tribes, carried on a settled agricultural life before they became nomadic. Of course the movements of these tribes were not confined entirely to what is now North Dakota.