gannett.] FORESTS EXPLORATION AND SETTLEMENT. 11 
progressively westward, the average being only 10 inches annually in 
the neighborhood of El Paso, in the western part of the State. The 
line of 20 inches of annual rainfall, which is the approximate limit of 
agriculture without irrigation, follows closely the foot of the Llano 
Estacado. The rain which falls in the eastern half of the State comes 
mainly, if not entirely, from the Gulf of Mexico, and descends most 
abundantly in the winter months, while that which descends upon the 
western part is derived mainly from the Pacific Ocean and comes 
largelv in the summer. 
FORESTS. 
PI. Ill, Jj, shows in a general way the distribution of . the forests 
of the State. The northeastern part is covered with forests of yellow 
pine, which are composed mainly of the short-leaved species, and which 
are valuable for lumber. West of this body two projections of wood- 
land enter the State from Indian Territory and run far southward into 
it. These are known as the Upper and Lower Cross Timbers. The 
timber consists of black-jack and post oak, which has no lumber value, 
but is used only for firewood and other minor purposes. The western 
and extreme southern parts of the State, except the higher mountain 
summits, are entirely devoid of tree growth with the exception of 
mesquite, which in some localities, as in the neighborhood of San 
Antonio, grows to arborescent size. The Llano Estacado is timberless. 
EXPLORATION AND SETTLEMENT. 
The exploration of Texas began shortly after the occupation of 
Mexico by the Spaniards under Cortez. The well-known expedition 
of Coronado is believed to have crossed the Panhandle and to have 
journeyed in a northeasterly direction to Kansas or Nebraska. The 
earliest settlers within the limits of the State came from Mexico. 
Between 1820 and 1835 many citizens of the United States entered 
Texas from the northeast and established themselves within its limits. 
The Texas revolution was engineered and the war for its independence 
was fought by these settlers from the United States. 
Shortly after Texas was admitted to the Union exploration began. 
The exploring expeditions were in charge of officers of the United 
States Army and were for the purpose of learning the resources of 
the country and discovering feasible railroad routes across the con- 
tinent. B} T these parties the State was traversed in numerous direc- 
tions and its principal topographic features were mapped. 
The subdivision of Texas lands has not resulted in the production of 
maps of much value. The coast line has, however, been mapped by 
the United States Coast and Geodetic Survey, and since 1884 large 
areas in the central and western portions of the State have been 
mapped by the Geological Survey. These areas altogether aggregate 
57,000 square miles, or more than one-fifth of the area of the State. 
