Why did the spanish built settlements in california?
The Pacific coast was valuable to Spain, because ships brought cargo from the Philippines, to Spanish Mexico and California, then across Mexico via Vera Cruz to Spain. However, Spain ignored the California coast for a long time (Though it was discovered in the early 1500s; note the ‘Sea of Cortes’ in Mexico), since Spanish attempts to land there were beaten off by the fierce natives. This lasted until Russians began settlement of the area in the late 18th century. Since California was then part of the Spanish Empire, these settlements contstituted a threat to the Empire. So Spain began colonizing; the main focus being missionary activity, combined with military fortifications.
