Original sentence: On August 3, 1769, Don José Gaspar de Portolà, the first governor of provincial California, and his entourage, the Portola expedition, became the first Europeans known to arrive in the area, having traveled an existing Indian trail (present-day Wilshire Boulevard) to the present-day site of La Cienega Park, named for a large swamp — "ciénega" in Spanish — and namesake of adjacent La Cienega Boulevard
Edited sentence: On August 3, 1769, Don José Gaspar de Portolà, back when California was part of Mexico, the first governor of provincial California, and his entourage, the Portola expedition, became the first Europeans known to arrive in the area, having traveled an existing Indian trail (present-day Wilshire Boulevard) to the present-day site of La Cienega Park, named for a large swamp — "ciénega" in Spanish — and namesake of adjacent La Cienega Boulevard