A. SETTING AND BACKGROUND
1. The Island General Geography and Geology
Guam is the southernmost and largest of the Marianas Islands, a north-south chain 420 miles long, extending from latitude 20°30' North, longitude 143°45' East (Farallon de Pajaros), to latitude 13°14' North, longitude 142°31' East (Guam). Formerly densely populated by the native Chamorros discussed below, Guam was occupied by Spain from 1668 to 1898, when it became United States territory, as it still is. The others of the Marianas, owned but not actually colonized by Spain, were purchased by Germany in 1899 and taken by Japan in the First World War, and now form part of the Trust Territory of the Pacific Islands, administered by the United States as a United Nations mandate. The other, smaller, southern Marianas, large only when compared to the tiny uninhabited northern islands, are Rota, Tinian (with the adjoining islet of Aguijan, where carnivorous snails are being tried out on the Giant African snail), and Saipan.
Guam, the only eighteenth century outpost of European civilization in the Pacific Ocean beyond the Philippines, the regular stopping-place between Mexico and Manila from 1565 to 1815, and today, since Philippine independence, the farthest outpost of actual United States territory in the Pacific, is the biggest single segment of Micronesia the largest island between Kyushu and New Guinea, between the Philippines and the Hawaiian Islands. Guam is approximately 30 miles long, 1 miles to 8-1/2 miles wide, and about 225 square miles in area. It is 1500 miles east of Manila, 1350 miles south of Yokohama, and about 3000 miles west of Honolulu, 5000 miles west of San Francisco.
The northern portion of Guam is a plateau flat but not horizontal, gradually sloping from somewhat over 500 feet above the sea on the east to 200-400 on the west, with steep cliffs on all sides toward the ocean, only occasionally broken by slopes or gaps or even readily negotiable trails, with small beaches of fine sand around the bays and coves between the high projecting points. The limestone plateau of the north, formerly densely forested but now virtually cleared of large trees, is without running water. The narrow waist of the island, from Pago Bay to Agana Bay, consists largely of swamp and small river valleys, and rather densely-grown or intensely cultivated low hills. The southern half is mountainous and surprisingly rugged, draining largely eastward into the Fena or Talafofo River, dropping to the sea in steep ridges and foothills and little valleys at numerous small bays, instead of high cliffs. Much of the south is covered by grassland. The island of Guam consists essentially of volcanic rook and coral limestone, enclosed by a fringing reef of coral. It is the southernmost and largest mountain of the submerged volcanic range which extends southward from central Japan, through the Volcano Islands and Bonins and Marianas, one of the arcs forming a continuation of the Aleutian-Kurile-Japanese chain of volcanoes. Guam is a large volcanic base which has been repeatedly elevated, on which coral limestone has repeatedly formed.
The entire northern half is a shelving, more or less flat, plateau of metamorphosed coral limestone, a terrace atop a submerged volcanic base. The limestone plateau is interrupted only by Mt. Santa Rosa (rising to elevation 870 feet from 600 feet m.s.l. at its base, with the surrounding plateau at between 500 feet and 600 feet), a comparatively recent small volcanic hill not an actual crater itself, but composed of volcanic rock. A second hill further south is of limestone, a bulge or a remnant Barrigada, 674 feet m.s.l., rising from a surrounding 400-foot level. The 200- to-500-foot cliffs bounding the plateau are very abrupt, nearly vertical, with only occasional breaks.
The southern half of Guam is mountainous and largely basaltic, a "volcanic massif which has burst through the coralliferous limestone" (Alexander Agassiz). Remnants of limestone formations as old as Miocene (over seven million years ago) are found occasionally, at considerable elevations, in the volcanic mountains of the southern half. Guam has been gradually and repeatedly elevated, apparently with submergences intervening.
The highest point on Guam is Mt. Lamlam, in the southwest, elevation 1334 feet. Other peaks of the rugged southern and southwestern portion rise to heights ranging between 1000 and 1275 feet.
Guam and the other southern Marianas (Rota, Tinian, Saipan) are relatively old islands weathered-volcanic combined with raised-coral type as against the unweathered, fresh, comparatively young, small volcanic peaks constituting the northern Marianas, a few of which are still alive as more or less active, at least smoking, volcanoes.
The island is closely encircled by a fringing reef, interrupted only at a few of the bays in the south and extending out to include Cocos Island, off the southwestern tip of Guam.
No references, notes, or citations are given for this section, as it is drawn partly from maps and from direct observation, partly from discussions with U.S.G.S. personnel working on Guam in 1952, and partly from non-technical, secondary, or general works, such as the following, which will also be referred to in connection with other topics:
Bowers, Neal M., "Chapter 8, The Mariana, Volcano, and Bonin Islands," in:
Freeman, Otis, ed., Geography of the Pacific, New York and London, 1951.
Oliver, Douglas L., The Pacific Islands, Cambridge (Harvard University Press), 1951.
Safford, William E., The useful plants of the island of Guam with an introductory, account of the physical features and natural history of the island of the character and history of its people and of their agriculture. Contributions from the U. S. National Herbarium, Volume IX, U. S. National Museum, Washington, 1905.
Thompson, Laura U., Guam and Its People, New York, 1947.
Last Updated: 14-Feb-2004