Which sentence segment contains a punctuation error?

"Yes I visited Crested Butte, Colorado, last winter," replied Mrs. Souza.

last winter,"

"Yes I visited

replied Mrs. Souza.

Crested Butte, Colorado,

And you think it's ... ?

I think that it is either "Yes I visited or last winter,"

But im not quite sure. I don't understand how to figure out how to do it. I just don't really understand it

http://grammar.ccc.commnet.edu/grammar/commas.htm

Scroll down and read the last section in #4 -- the section just before #5 begins. You'll see it clearly.

The correct sentence segment without a punctuation error is "Crested Butte, Colorado,". The punctuation error is found in the segment "last winter,".