99 points/ what is a topographic map? what mountain range is in the east of the usa? what major mountain range is in the west of the usa? why were these mountains barriers in the past? list 2 reasons why they would have been barriers.

Topographic map: It has markings to show points of elevation like mountains and extremely tall trees.

West: Rocky Mountains

East: Appalachian Mountains

Reasons why they would have been barriers in the past.

They haven't mapped out the mountain so they don't know where they are going or where the best path is. There aren't any points of reference because, no one thought to do it. The rough terrain and the trouble like mountain lions they might encounter while crossing the mountain.  The weather would just make it worse. That is why it was such a good isolation barrier for people like in China in the ancient times.

Explanation:

where are the statements without that i cant you

heat from the core of the earth causes convection currents to occur in the mantle. these currents slowly move the crust around.