On a rugged island just offshore from Ventura County, archaeologists have turned up evidence of some of the oldest human activity in coastal Southern California. On Santa Cruz Island, the largest of the Channel Islands, researchers have found three sites scattered with ancient tool-making debris and the shells of harvested shellfish. The youngest of the three sites has been dated to 6,600 BCE, but based on the types of tools found at the other two, archaeologists say they may be as much as 11,000 to 12,000 years old. The artifacts are traces of what's known as the Island Paleocoastal culture,...