Error Correction

I'd add a comma after 'coast':

moved from the Altlantic coast, across ...

I'd add 'of' after 'miles':

3,000 miles of forests, ...

European settlers in North American moved from the Atlantic coast, across 3,000 miles of forests, grasslands, deserts, and mountains until they reached the Pacific Ocean.

Adding 'of' after 'miles' sounds make sense, but can you explain it?

And, I don't think we need comma here after 'coast'.
European settlers in North American moved (from the Atlantic coast) across 3,000 miles of forests...

'Miles of forests, grasslands, etc' -- just as we have 'pounds of tomatoes' and 'acres of rice', Jeff. the 'of' is there to describe the nature of the 'miles'.

I understand your point about the comma-- it is not really required--, but I think Casi is right that it works well here, to help create the image of the vast crossing-- and I would even add another comma, I think, after 'mountai

Hehe Now it downed on me.

You know, it's not easy to find out, sometimes we even have the silly question like this: putting 'a' before the word with the first letter pronounced as a vowel. And it's easy for us to skip it over. hehe

Hehe Now it dawned on me.

You know, it's not easy to find out, sometimes we even have the silly question like this: putting 'a' before the word with the first letter pronounced as a vowel. And it's easy for us to skip it over. hehe