Mailing a standard-size letter from California to Arizona, or to any location within the United States via the United States Postal Service, takes one stamp. Letters that are non-standard sizes, or those that weigh more than an ounce, require additional postage.
As of 2014, a First-Class stamp for a 1 ounce letter costs 48 cents. Large flat envelopes cost 98 cents to mail. The same letters can be sent as Certified Mail from California to Arizona or anywhere else in the United States for an additional $3.30.
Sending a letter by Priority Mail, which provides free tracking, costs $5.05. Overnight by Priority Mail Express costs $13.09. These extra charges may entail more stamps or other printed labels showing the charges.