RIO DE ORO, a Spanish possession on the N.W. coast of Africa. It, is bounded W. by the Atlantic, E. and S. by Saharan territory under French protection. The northern frontier, where the protectorate adjoins the territory of the semi-independent tribes south of Morocco, is undefined. The most northerly point claimed by Spain on the coast is Cape Bojador. The southern and eastern boundaries were defined by at Franco-Spanish convention in 1900. The frontier traverses the middle of the Cape Blanco promontory, then runs eastward along the parallel of 21° 20′ N. till it meets the meridian of 13° W., whence it turns first N.W. and afterwards N.E., meeting the tropic of Cancer at 12° W. and thereafter runs due N. Forming part of the Sahara, Rio de Oro is nearly waterless; Oases are few and the sparse population consists almost entirely of nomad Arabs and Berbers. They are Mahommedans. In the south is the hilly country called Adrar Suttuf, not to be confounded with Adrar Ternur (see Adrar and Sahara). The estimated area of the protectorate is 70,000 sq. m.
The peninsula of Rio de Oro, where is the principal Spanish settlement, occupies the central part of the coast-line in 23° 50′ N., 16° W., and is united to the mainland by a sandy isthmus. Its length is 23 m., its breadth 114 to 2 m. and it is on an average about 20 ft. above sea-level. The bay between peninsula and mainland—the so-called Rio de Oro—is 22 m. long, 5 broad, navigable over two-thirds of its extent, with good anchorage in most of the channel, but the bar at its mouth is not always easy to pass in rough weather. The peninsula has very sparse vegetation, except in its southernmost part near Cape Durnford. At the head of the, bay is a small island—Isla Herne.
The climate is generally temperate, and not unhealthy except in the autumn. Esparto grass and manzanilla are grown in many places, but European plants are not easily acclimatized. On the peninsula and in the neighbouring country there are many wolves, foxes, hyenas, gazelles, lizards, hares, pelicans and large crows. The natives rear cattle, sheep, camels, and have but few horses. In contrast with the sterility of the land the sea throughout the coast of Rio de Oro abounds in fish, especially cod. The fishing industry is in the hands of the Canary Islanders and of the French.
The estuary between the mainland and the peninsula was taken by its Portuguese discoverers in the middle of the 15th century for a river, and, obtaining there a quantity of gold dust from the natives, they named it Rio d’Ouro (Gold River), Rio de Oro being the Spanish form. At a spot about 50 m., inland from the head of the estuary a Portuguese trading station was established, of which ruins exist, but the activity of the Portuguese was before long transferred to the true auriferous regions of the Gulf of Guinea.
Spain’s interest in the Saharan coast dates from the 13th century, but was particularly directed to that part nearest the Canary Islands, a strip of coast over which she now exercises no sovereignty. The site of the fort of Santa Cruz de Mar Pequena, established in 1476, though not identified, was north of Cape Bojador. The protection of the Canary Islanders engaged in the fisheries south of that point occasioned, however, the presence of Spanish warships in these waters, and small trading stations were formed at Rio de Oro, Cape Blanco and elsewhere. To preserve the interests thus acquired, Spain in January 1885 took the territories on the coast between capes Blanco and Bojador under her protection. The year before the Hispano-American Company had built a trading station on Rio de Oro peninsula, but in 1885 it was destroyed by the natives. The company renewed its operations, but subsequently ceded its rights to the Transatlantic Company of Barcelona. The extension inland of Spanish influence was opposed by France, which claimed a protectorate over the Sahara. The conflicting claims of the two powers were finally settled by the convention of 1900, which fixed the frontier in the manner stated. The administration is carried on under the control of the captain-general of the Canary Islands.
RIO GRANDE, a North American river, which rises in the
San Juan Mountains of southern Colorado, flows S.E. and S.
in Colorado, S. by W. and S.E. through New Mexico, and S.E.
between Texas and Mexico to the Gulf of Mexico. Its length
is approximately 2200 m., and for about 1300 m. it forms the
international boundary between the United States and Mexico.
It presents many features of a complex physio graphic type,
being first a river of the Rocky Mountains, then of the interior
desert sand then of the Atlantic Coastal Plain. It also
presents a complicated geological history, as it includes what
were originally several distinct streams. The Mexicans call
it the Rio del Norte in its upper course, the Rio Bravo in the
“Big Bend,” from the mouth of the Conchas river to the
mouth of the Devils river, and the Rio Grande only in its
course through the Coastal Plain. From its headwaters,
12,000 ft. above the sea, it rushes rapidly down a mountain
canyon to San Luis Valley, in Colorado. It flows with moderate
speed through this broad valley, enters a long canyon with a
maximum depth of 400 ft., about 4 m. above the boundary
between Colorado and New Mexico, and is hemmed in between
canyon walls rising as high as 1000 ft. or between the sides
of narrow mountain valleys throughout its course through
New Mexico. It passes through a series of picturesque
canyons, some of them 1750 ft. in depth, in the “Big Bend,”
and becomes a silt-laden stream with a shifting channel in
its passage through the Coastal Plain. Except in the flood
season of May and June, the quantity of water which, for
irrigation and by evaporation, is taken from the Rio Grande
between its entrance to the San Luis Valley and the mouth
of the Conchas, is greater than that received, and as a consequence
it is an intermittent stream in this region. The
flow of the Conchas is constant, and in the “Big Bend” the
volume of the Rio Grande is enhanced by springs which break
out in the bed. The total flow of the Rio Grande is ten times
greater in some years than in others, and when its waters have
been highest there have been great floods in its lower course
and so much shifting of its banks as to cause international
complications. Even in its course through the Coastal Plain
its channel is so much obstructed by sand bars that it is of
little importance for navigation. As the increasing diversion
of the water of the Upper Rio Grande for irrigation in Colorado
and New Mexico resulted in a scarcity of water for this purpose
in Mexico, that country complained, and to remedy the evil
the Reclamation Service of the United States proposed the
construction by the United States of a storage dam across
the river near Engle, New Mexico, which would form a storage
reservoir having a capacity of 2,000,000 acre-feet and from
which Mexico should be furnished with 60,000 acre-feet of
water annually. Mexico agreed to this proposal and a treaty
covering the matter was proclaimed in January 1907. The
principal towns and cities on the river are: Brownsville,
Texas; Matamoros, Mexico; Laredo, Texas; El Paso,
Texas; and Ciudad Juarez, Mexico.
RIO GRANDE DO SUL, a southern frontier state of Brazil,
bounded N. by the state of Santa Catharina, E. by the Atlantic,
S. by Uruguay and W. by Uruguay and Argentina—the
Uruguay river forming the boundary line with the latter.
Area, 91,333 sq. m. Pop. (1900) 1,149,070, an increase of
251,615 since 1890. The northern part of the state lies on the
southern slopes of the elevated plateau extending southward
from São Paulo across the, states of Paraná and Santa
Catharina, and is much broken by low mountain ranges whose
general direction across the trend of the slope gives them the
appearance of escarpments; A range of low mountains extends
southward from the Serra do Mar of Santa Catharina and
crosses the state. into Uruguay. West of this range is a vast
grassy plain devoted principally to stock-raising—the northern
and most elevated part being suitable in pasturage and climate
for sheep, and the southern for cattle. East of it is a wide
coastal zone only slightly elevated above the sea; within it
are two great tide-water lakes—Lagôa dos Patos and Lagôa
Mirim—which are separated from the ocean by two sandy,
partially barren peninsulas. The coast is one great sand
beach, broken only at one point—that of the outlet of the two
lakes, called the Rio Grande, which affords an entrance to
navigable inland waters and several ports. There are two
