Immigration rules for visiting San Felipe are clear. Most visitors do not need a Mexican visa. You will need an FMM Tourist Card unless your stay is under seven days.
If you drive to San Felipe for less than a week, you can cross without paying. You are still required to carry the card. For longer visits, stop at the Mexicali Immigration Office as you cross from Calexico into Mexicali. Present your passport or passport card. Pay the fee at the bank next door. The cost is about 332 pesos or $20 USD. The card is valid for 180 days and can be renewed by paying the fee again.
Mexico is preparing an online system for buying the FMM Tourist Card in advance. The site is in Spanish.
To return to the United States, you must show documents. A U.S. passport or passport card, or a birth certificate with photo ID, is accepted. Foreign residents of the U.S. must show their Green Card and passport from their home country. Since 2009, all travelers entering the U.S. are required to have a passport or passport card.
If you plan to live in Mexico long-term, for retirement or business, you need a Mexican resident visa. The process is standardized but complex. Work with a qualified local advisor.
The San Felipe Immigration Office is located at the Glorietta traffic circle on the right as you leave town. They are open Monday through Friday from 9 a.m. to 2 p.m. The phone number is +52 686 577 1083.