The pocket gopher is principally nocturnal or crepuscular but sometimes it is active at midday, especially if the day be dark and cloudy. Pocket-gopher activity is indicated by fresh mounds of earth on the surface of the ground. Rarely, an observer may see movement of plants as the gopher molests the roots of the plants, or even see the head and shoulders of an animal that partly emerges from an open burrow. The ordinary gopher mound consists of less than a cubic foot of earth. The earth is forced up from a single opening and usually is pushed out in one direction. In consequence it forms in a fan-shaped pile about the opening, and the last load forms a circular plug above and to one side of the burrow opening. When so much earth has been forced out of one opening that expulsion of additional loads of earth is overly difficult, the burrow is extended slightly to one side, or even extended into the newly formed mound, and another fan formed. Usually not more than three coalesced fans form a mound, but where the soil is exceedingly soft and fluffy, hundreds of fans may form a composite mound and the one mound may include a cubic yard of earth. Large composite mounds probably are formed gradually over a period of weeks or even months. The earth in a fresh gopher mound is usually "scratched," and gives the appearance of having been sieved. Pebbles weighing more than 100 grams are included in material ejected from burrows. The entrances to the burrows of gophers are usually solidly plugged with earth. The plug may be from a few inches to more than a foot in length. At times a burrow entrance may appear to be open, but in such cases investigation will usually reveal it to be plugged some distance back--sometimes several feet. In contrast to the gopher mounds described above, the mounds of moles are not fan-shaped but volcano-shaped. The earth from a mole's burrow is forced straight upwards, whence it falls to either side. Later loads are pushed up from beneath, raising the entire mound, with the last material ejected at the center and bottom. The earth of a fresh mole-mound is not of fine texture but instead is "clotted" and, if damp, gives the mound a fractured appearance. When mounds are older, perhaps changed by rain and sun, their identity as of mole-origin or pocket gopher-origin is more difficult to establish. In such cases, if no fresh mounds can be found, the observer must rely on the spacing of the mounds. Mole-mounds are spaced along a burrow, about as far apart as a man can step. Gopher mounds are irregularly spaced, and the course of the burrow cannot be traced merely by observing the arrangement of the mounds as can that of the mole.