In the mid 1500's, the Chumash probably became aware, through their trading partners, of the Spanish explorers who were coming into New Mexico and Colorado. Later in the century, large canoes "with clouds on them that moved without paddles" began to appear. The first of these was the Cabrillo expedition from Mexico in 1542. The second may have been the Englishman, Sir Francis Drake, who may have sailed the Chumash coast and spent five weeks repairing his ship, the Golden Hinde, in the lagoon in 1579. In 1602, the Viscaino expedition stopped by the Goleta Valley and the nearby Chumash village of Mikiw, known today as Dos Pueblos.

One hundred sixty-seven years later in 1769 the Portola expedition, sent by Spain to colonize the northern territories, passed through the Goleta Valley.

The soldiers were impressed by the island in the middle of the lagoon and they named it Mescaltitlan after a similar island in their home province of Nayarit, Mexico. The Portola expedition established presidios and mission churches at San Diego and Monterey. The missionaries took possession of the land and held it in trust for the Indians.