If you travel across the United States on a line from North Carolina to Southern California, you will find that temperate forest extends from the East Coast westward for approximately 1,200 miles to about the valley of the Mississippi River. There it begins to thin out toward the west into oak savannas and finally gives way entirely to open grassland (Great Plains), which extends another 1,000 miles westward up into the foothills of the Rocky Mountains. If you cross over the mountains you find chaparral in Southern California. True/False
The single most important factor affecting the type of biome present in each of these major regions of the United States is rainfall.