Imperial Valley, fertile region in the Colorado Desert, SE Calif., extending S into NW Mexico. Once part of the Gulf of California, most of the region is below sea level; its lowest point is -232 ft (-71 m) at the southern shore of the Salton Sea. Receiving only c.3 in. (7.6 cm) of rain annually, the valley experiences extremely high temperatures (115°F;/46°C;) and has a great daily temperature range. Having one of the longest growing seasons in the United States (more than 300 days), the valley can, with irrigation, support two crops a year; it was first irrigated in 1901. Several disastrous floods on the Colorado River in 1905-6 inundated the area; not until 1936, with the completion of Hoover Dam, was the valley safe from floods. Approximately 1 million acres (404,700 hectares) have been irrigated, chiefly by the All-American Canal. The valley is an important source of winter fruits and vegetables for the northern areas of the United States; cotton, dates, grains, and dairy products are also important. Brawley, Calexico, and El Centro, Calif., are the main U.S. cities in the valley; Mexicali, Mexico, also in the valley, is the center of Mexico's important cotton-growing district.

Imperial Conference, assembly of representatives of the self-governing members of the British Empire, held about every four years until World War II. The meetings prior to 1911—in 1887, 1897, 1902, and 1907—were known as Colonial Conferences, and were chiefly concerned with defense problems and the possibility of imperial tariff preference. Relatively informal, they were held when colonial representatives came to Great Britain for royal celebrations. More formalized meetings were held in 1907, 1911, 1917-18, 1921, 1923, 1926, 1930, 1936, and 1937. The conferences were designed to strengthen imperial ties by exchange of ideas, but their decisions had no legal effect. The two main focal points of discussion remained defense and economic policy. In 1917-18 the Imperial War Conference acknowledged the importance of the whole empire in defense policy by admitting India, not yet self-governing, to the conference. There was an acknowledged need on the part of Britain for practical support from the dominions in military and naval resources, and a parallel desire for participation in the decision-making initiative on the part of the dominions. The dominions also wanted to be able to pursue independent foreign policies, within the bounds of imperial cooperation. The constitution of the conferences themselves and the status of the dominions were the chief problems discussed at meetings during the 1920s. The resolutions of the conferences were given legal effect by the Statute of Westminster (1931; see Westminster, Statute of), which declared the legislatures of the several dominions on an equal footing with that of Great Britain. A standing Imperial Economic Committee concerned itself with coordination of economic matters. After World War II, it was replaced by the biennial Conference of Commonwealth Prime Ministers and yearly meetings of finance ministers.

Imperial Beach, residential and resort city (1990 pop. 26,512), San Diego co., S Calif., on the Mexican border; inc. 1956. The southwesternmost city in the continental United States, Imperial Beach is near several naval and air stations.

British Imperial System of weights and measures: see English units of measurement.

Valley extending from southeastern California, U.S., to Mexico. It forms part of the Colorado Desert. Intensive irrigation began in 1901 with the opening of the Imperial Canal, which diverted water from the Colorado River. Floodwaters in 1905–07 destroyed the irrigation channels and created the Salton Sea. The valley is now watered by the Hoover Dam and the All-American Canal. With 3,000 mi (4,800 km) of irrigation canals, it contains 500,000 acres (200,000 hectares) of cultivated land.

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