The Spanish empire and its agent José de Gálvez founded the port of San Blas, Nayarit in order to communicate with the Californias. However, the site is not particularly favorable and it did not remain an important port. The empire had better Pacific ports at Acapulco, Guaymas, and Mazatlan. What made founding a new port at San Blas seem better than expanding one of those?
The Wikipedia article for San Blas seems to address this(emphasis mine):
San Blas's location was useful and logical, however, because it minimized travel time from Guadalajara and Mexico City without increasing the total distance to the Californias. Also, the area around San Blas had a plentiful supply of hardwoods useful for ship building and repair. Fresh water was also available year round.
The water supply found here was considered important enough to be discussed in this 1870 publication:
The watering place is at the northern extremity of a large open bay south of San Blas the beach is shoal and the casks have to be rolled 300 or 400 yards through the jungle to a stream of water This stream during the spring tides is occasionally brackish but we succeeded in obtaining supplies by immersing the empty cask with the bung in such a position that only the fresh water which of course would be on the surface could enter By rigging triangles with spars in such a position that the boats could go under them to load we succeeded in embarking daily 32 tons of water