Chilkoot or Dyea Dave in Skagway??

[ISLABONITA]

Passport requirements in detail say a passport card for a US citizen is valid enough for entry into Canada and US and is $30 .
Check the government website.
If you also have an expired passport take it with you.

[ashbris]

Thanks to everyone that replied. I used the link and worked my way through what you needed to have on a closed loop cruise and this is the answer from US Custom & Borders page. Maybe it well help someone else also!

U.S. Citizens on closed-loop cruises will be able to enter or depart the country on the cruise with proof of citizenship, such as an original or copy of his or her birth certificate (issued by the Vital Records Department in the state where he or she was born) and, if 16 or older, a government issued photo ID. If the child is a newborn and the actual birth certificate has not arrived from the Vital Records Department, we will accept a Hospital issued birth certificate. The United States does not require you to have a passport. (A Consular report of Birth Abroad issued by the Department of State or a Certificate of Naturalization is also acceptable.)