Unit 6

Chapter Twelve

The Western Mountains

lava hot, melted rock rock that comes from a volcano
volcano an opening in the Earth’s surface out of which hot gases, ash, and lava may pour out
slope the side of a mountain

Continental Divide 

an imaginary line that runs north and south along the highest points of the Rocky Mountains
timberline
 on a mountain, the elevation above which the temperatures are too low for trees to grow
barrier

something that blocks the way or makes it hard to move from place to place
transcontinental railroad

a railroad built to link the East and West coast of North America
labor work
satellite an object that orbits the Earth
mileage table a table that gives the number of miles between the listed cities
boomtown towns that grew up quickly, almost overnight
trade-off the giving up of one thing  in order to get another
opportunity cost the value of the thing a person gives up in order to get something else
public land land that is owned by the government
geyser a spring that shoots steam and hot water into the air
terrace a flat “shelf” dug into the mountainside
bartering trading of one kind of good for another without using money