Life in Mesa Verde, as in all the Pueblo area, depended on agriculture. There was dry farming on the mesa tops, but irrigation was particularly well developed here.[7] A broad, shallow ditch, some four miles long, and with a very regular gradient has been found on the Mesa Verde. Apparently water was turned out on the cornfields from this ditch. There were also check dams which caught the run-off of heavy summer rains and made it available for the crops. They served a further purpose in conserving soil which might otherwise have been washed away. Reservoirs were present and must have also provided water for the fields, but they have not yet been studied sufficiently for us to have much information as to their construction or use. Mesa Verde pottery is as distinctive as its architecture. Fine corrugated vessels were made, and a small percentage of imported red pottery was present, but the outstanding ware was black-on-white. This pottery has certain distinctive features which make it easy to recognize. The walls are fairly thick, and rims tend to be square and flat. The background is a pearly white with grayish undertones. Most vessels have been so carefully polished that they have a glossy surface which sometimes almost gives an impression of translucence. The decoration, applied with black paint, is usually in the form of geometric patterns, although a few bowls show life-forms in their designs. Band patterns were extremely common, and many large solid elements as well as hatchured patterns were used. The latter tend to be much coarser than those on Chaco pottery. The most distinctive forms were flat-bottomed mugs, which resemble beer steins, and “kiva jars.” The latter are vessels in the form of a somewhat flattened sphere, with fitted covers resting on an inner rim, as do those of modern sugar bowls. There were also many bowls, ollas (water jars), ladles, canteens, and seed jars. [Illustration: Fig. 32—Mesa Verde black-on-white pottery of the Great-Pueblo period. (Courtesy Mesa Verde National Park.)]