Clovis culture

The Clovis culture was one of the first well documented Native cultures in the Americas. The Clovis people lived in the Americas about 13,000 years ago. They lived there for between 200 and 800 years. Different sources list different lengths of time in that range.
They had a special way of making tools like spear tips and knives from stones. The flint tips are called Clovis points. Artifacts that they made in this way can be found in many places in North America. The Clovis way of making tools only lasted between 500 and 1000 years. After that, other similar ways became more popular. 
They are called "Clovis culture" because archaeologists first found their artifacts at Clovis, New Mexico.
The end of the Clovis culture.
A decline in the availability of megafauna, together with the population becoming less and less mobile, led to local differentiation of lithic and cultural traditions across the Americas. After this time, Clovis-style fluted points were replaced by other fluted-point traditions (such as the Folsom culture).
Clovis First (a theory).
The Clovis First theory says that the Clovis people crossed the Beringia land bridge over the Bering Strait from Siberia to Alaska during the period of lowered sea levels during the ice age, then made their way towards the south, through an ice-free corridor east of the Rocky Mountains in present-day Western Canada as the glaciers retreated.
Things that point to earlier settlement of the Americas.
"Clovis First" is one of the theories about the Settlement of the Americas. There are other ideas and research that go against "Clovis First".
Research that shows human habitation before the Clovis culture.
Archaeological sites that have been shown to be older than the Clovis culture: