POWER OF ATTORNEY

I, Aida Alvarez, do hereby constitute and appoint Joseph S. Konowiecki,
Michael E. Jansen and Ellen K. Erickson, or each one of them separately,
as my true and lawful attorneys and agents, to do any and all lawful acts
and things in my name and on my behalf, and to execute any and all
instruments, forms or filings in my name and on my behalf, which said
attorneys and agents, or each one of them separately, may deem necessary
or advisable in order for me to comply with the disclosure requirements
of Section 16(a) of the Securities Exchange Act of 1934, and any related
rules, regulations, and requirements of the Securities and Exchange
Commission; and do hereby ratify and confirm all that said attorneys and
agents, or each one of them separately, shall do or cause to be done by
virtue hereof.

Date:  May 17, 2004

Aida Alvarez