LOCATION AND SIZE

Most of Costa Rica lies between parallels 9 and 11 north latitude, and meridians 83 and 86 west of Greenwich. The northern part is more than one degree south of the extreme northern part of South America. At the narrowest place the country is about 80 miles wide, from the Atlantic coast to the Pacific. The area is usually given as between 18,000 and 23,000 square miles. The region considered in the present paper extends from the Atlantic coast to Cartago, a distance of 70 miles, and from the Sixola Valley on the south to Guacimo on the north, a distance of about 45 miles. Some things outside of this area are discussed, but, unless otherwise designated, the area mapped in figure 1 is meant.

MOUNTAINS

The dominating factor in the geography of Costa Rica is a mountain range that occupies more than half of its area. It trends southeastward from the northwestern corner of the country to the southeastern. The mountains are almost entirely volcanic in origin and some of the volcanoes are still active in a mild way. The highest mountain, Chirippo, about 12,300 feet in elevation, is in the southern part of the country. An important group of peaks, including the active volcanoes Irazu, 11,300 feet, and Poas, 8,620 feet, lies in the central part near the capital, and from this group the elevations gradually decrease to the northwestern corner where Orosi, 5,120 feet in elevation, is located. The main peaks are active, or extinct, volcanoes and they make the sky line jagged.

From the coastal plain near Limon the mountains rise steeply from an elevation of 1,000 feet or less to 11,000 feet in 15 miles. South of Limon the rise is much more gradual and a considerable area of dissected plateau intervenes between the coastal plains and the mountains.

COASTAL PLAIN

East of the mountains the topography is nearly flat, consisting of a coastal plain of little relief. From the southeastern part of the coast line nearly to Limon the plain varies between two miles and five miles in width. From 10 miles south of Limon the interior border of the plain runs northwestward and the plain widens to 70 or 80 miles along the San Juan River. The plain is made up of alluvial fans, and numerous streams cross it. As is always the case in alluvial fans, many of the streams give off distributaries and abandoned channels are common. The landward edge of the plain rises northward as the plain widens. Near the mouth of the Estrella River the inner edge is not more than 40 feet high, whereas at Guapiles, at the extreme northwest of the map shown in figure 1, it is about 1000 feet high.

Much of the wide coastal plain is under flood water a part of every year and has never been reclaimed for crops. Swamps and jungle predominate. The vegetation and stream conditions in the areas that have been farmed are represented in figures 7 and 9, photographs of the Matina River near Matina and the Siquirres River near Siquirres. The 200 meter contour line on the map, figure 1, is near the boundary of the coastal plain save in the northwestern part of the map, where the coastal plain boundary reaches to the 400 meter contour. The map1 of Treadwell,

1 Possibilities for para rubber production in northern tropical America: Dept. Commerce, Trade Promotion Series, no. 40, fig. 12, 1925.

Hill, and Bennett, to which reference is made in another place, represents the coastal plain area as accurately as possible until better surveys have been made.

STREAMS

Streams are numerous but none of them is large. The San Juan River on the northern boundary is the only stream that is navigable for even a short distance. Most of the streams flow in almost direct courses to the Caribbean Sea and do not receive many tributaries, and most of them have rapids to within a few miles of their mouths. At their mouths they have bars and the water is too shallow for boats larger than gasoline launches.

The most important stream between the northern and southern boundaries is the Reventazon River, which rises at the continental divide near San Jose and flows north and east to empty into the Caribbean about 30 miles north of Limon. The distance from source to mouth is about 70 miles, but the length of the river is about 200 miles. From near Cartago to Siquirres on the coastal plain it flows in a deep narrow valley, canyon-like in many places. Through long reaches the flood plain is lacking or is little wider than the stream, and the top of the valley is not distinct, but blends with the mountain sides. This valley forms the only means of communication through the steep, high mountains between the coastal plain and the inland plateau. Through most of the deep valley the stream is 100 to 200 feet wide but in places narrows to 50 feet. It consists almost entirely of rapids and is impassable even for small canoes. It forms an almost impassable barrier for the inhabitants, and the country is uninhabited on the south side of the sream between Siquirres and Turrialba, although the railroad runs along the north side for nearly 50 miles.

Below Siquirres, on the coastal plain, the Rventazon broadens and in about six miles becomes large enough to be navigated by small launches. The length of the river from Siquirres to the Caribbean is probably 40 miles, though the distance in a straight line is only about 15 miles. In that distance the river gives off many distributaries but receives no tributary of importance, excepting the Parismina. (The Reventazon Valley is described more fully on page 00.)

The Chirripo River rises in Chirripo Mountain near the southern boundary and flows slightly east of north to empty into the Caribbean about 18 miles southeast of the mouth of the Reventazon. The distance from source to mouth is about the same as that of the Reventazon, but its course is more direct and its length not more than 150 miles. It carries about half as much water as the Reventazon and its valley is canyon-like from its source to the base of the low mountains about 25 miles southwest of Limon. After it emerges from the mountains it is joined by the Barbilla from the southwest, and the combined streams are called the Matina. The Matina is much like the Reventazon below Siquirres, banks low, stream sluggish, the surrounding land inundated part of each year (see figure 7).

About 20 miles southeast of Limon the Estrella River enters the Caribbean Sea. Its flow seems to be more than half as much as that of the Reventazon, but it has frequent rapids to within three miles of the sea. Near its mouth low mountains approach to within one mile of the sea. The general course of the Estrella is eastward to within 10 miles of its mouth, where it turns to the northeast. Canoes are used on the lower three or four miles of its course. The main valley of the Estrella is west

of a gap through the low ranges of mountains near the coast, where it is five or six miles wide and contains some of the best banana lands.

The Sixola2 River, which forms part of the southern boundary of Costa Rica, has a general easterly course near the ninth parallel. It is larger than the Reventazon but is not navigable even in the lower 10 miles of its course, except for launches. Forty miles from the Caribbean it issues from a canyon in the mountains into a valley several miles wide where some of the finest banana farms in Central America are located.

Between the Reventazon and the San Juan several streams have been mapped, but little is known concerning them. All of the streams north of the Estrella flow in remarkably parallel courses and receive few tributaries.

COAST LINE AND PORTS

The eastern coastline of Coasta Rica is remarkably uniform. No bay worthy of the name indents it, no large river mouth cuts it, no islands diversify it, no natural harbor makes it inviting. It is a typical coast of a rising land. Other evidences than the coast line that the land is rising are ledges of coral a few feet above sea level and recent sediments containing modern shells several feet above sea level. The even coast line without indentations is one reason for the lack of towns along the coast.

Limon is the only port on the eastern coast that gives anchorage to ocean going ships or is equipped to load them. The harbor is unprotected, but winds are only rarely strong enough to cause inconveniences to ships at the piers. Two wooden piers give anchorage space to four boats of 10,000 tons. The piers are equipped with railroads and more than 300 freight-car loads of fruit are sometimes loaded on shipboard3 in one day. No other town on the eastern coast has harbor equipment of any kind. Almirante, in northern Panama, serves as a port for the Sixola Valley district of southern Costa Rica. At this port the piers are equipped to load four boats of 5,000 to 10,000 tons at the same time and railway tracks run onto the piers. The port is in a well-enclosed bay and is much more favorably situated than Limon. Coral reefs shut in part of the bay and leave only rather limited space for ships to pass through. A small boat which runs between Bocas and Almirante goes through one gap in the reef where the channel is not more than 50 feet wide and the reefs come nearly to the surface of the water. Nearly 40 per cent of the bananas exported from Costa Rica go by way of Almirante. The Costa Rican shipment through this port in 1918 was 2,942,164 stems, but this port also handles all of the bananas of northern Panama.

CLIMATE

RAINFALL

The officials of the United Fruit Company kindly allowed the writer the use of rainfall data records of 1907 to 1920 at Santa Clara and of 1915 to 1920 at the five other places listed below.

2 Also called Teliri, Tiliri, Tariri, Sixaola, and Talamanca. The writer has not seen "Talamanca River" on a map, but Olsson uses the name many times and it is in common use in Costa Rica. (Olsson, A. A., The Miocene of northern Costa Rica: Bull. Am. Paleontology, vol. 9, no. 39, 1922.)

3 According to Bergsmark an iron pier now affords accommodation for vessels. Bergsmark, Dan., Geographic provinces of Costa Rica: Journal of Geography, vol. XXVI, p. 311, 1927.

The average rainfall per month for the years 1915 to June, 1920 for Bananito River, Estrella, Limon, Zent, Santa Clara, and Indiana was as follows:

There is no regular wet or dry season in eastern Costa Rica. The months of least rainfall are January, February, March, April, and September, in modal years, but in 1916 January had the heaviest rainfall of any month, the average for six places being a little more than 20 inches. In 1915 February was second only to May with an average of more than 16 inches. In 1917 March had a rainfall of more than 18 inches and was second only to November. April's highest rainfall recorded was in 1919 with about 12 inches and its rank was sixth. November's average of about 17 inches is the highest for any month. September's average is the lowest, and it has no record of a fall above eight inches. In the five-year record it ranks next to the lowest three times, third once, and eighth once, and its average in six places for five years is 6.5 inches. From 1908 to 1915 the Santa Clara record is exceptional, being about 13 inches for each September. From 1916 to 1920 its September average was about five inches.

The general belief of the inhabitants is that the months of least rainfall are January to June. The highest record for one month is 47 inches, for December, 1908. May, 1918, had 27 inches, July, 1918, had 28 inches, August, 1909, had 30 inches, November, 1917, had 41 inches, January, 1910, 25 inches, April, 1910, 20 inches, May, 1914, 35 inches, August, 1914, 28 inches.

The five-year record shows an average of 125 inches per year. The highest record is 218 inches at Santa Clara in 1914.

The rain may come in heavy downpours or in an almost steady fall of about an inch per day. Thirteen inches in one day is a record for the years later than 1907. The daily shower is not common in Costa Rica and rain is as common at night as during the day. Only rarely thunder accompanies the rains.

The exceptionally heavy rainfalls give rise to destructive floods, though the average fall does not cause the streams to rise to flood stages. West of Guapiles, where the rainfall seems to be heavier than at the recorded stations, floods were so destructive that the railway line to San Jose was abandoned and its former course is completely lost for many miles.

The rainfall of Costa Rica does not correspond to that of the tradewind belt, but is more like that of the equatorial belt. The general atmospheric drift must be westward from December to May, as that constitutes the dry season west of the mountains. At Guanacaste the record of rainfall from 1903 to 1915 shows no fall in 47 out of 52 months of January to April, and there was no rainfall in 9 of the 13 Januaries. November is a dry month, the usual fall being about one inch. The average yearly rainfall at Guanacaste is 55 to 60 inches. October is usually the month of heaviest fall.