San Carlos has no airport of its own. The main options are:
By air to Guaymas/Empalme: General José María Yáñez International Airport (GYM), served by flights from Mexico City and a few US cities. San Carlos is 15 kilometres from the airport; taxis and car rental are available.
By air to Hermosillo: General Ignacio Pesqueira García Airport (HMO) is a larger hub with more connections, including direct flights from several US cities and major Mexican airports. The drive to San Carlos takes about 1 hour 45 minutes on a fast toll road.
By road from the US border: The crossing at Nogales (Arizona–Sonora) is the most direct route from the US. From the border to San Carlos is roughly 400 kilometres — about four hours on Highway 15 south, a fast divided highway for most of its length. The route passes through Hermosillo. You will need Mexican vehicle insurance, which cannot be purchased at the border; buy it in advance online.
By bus: First-class buses (TAP, Tufesa) connect Guaymas to Hermosillo, Nogales, and Mexico City. Local taxis and colectivos cover the 15-kilometre hop from Guaymas to San Carlos. Direct bus service to San Carlos itself is limited.