At this point not much is known of what happened. In between Woodland, WA and Westport, CA are the entire state of Oregon and much of California.
Their route is easily inferrable from the geography (using Google Maps) and the two days it took them to get to Westport. They would have driven south on I-5 and crossed into OR at Portland (on I-5) or between Portland and Gresham (I-205). They would have continued south on I-5, through OR's Willamette Valley and the Cascades (Grants Pass and Medford), crossing into CA just south of Ashland. Then they probably continued south on I-5 past Lake Shasta to Redding. At Redding they probably turned west on California Highway 299 (SR299), reaching Humboldt Bay and US101 at Arcata. They probably followed US101 through that part of the Coast Range to Leggett, where they took SR1 to the coast, a bit north of Rockport. At Hardy, a couple of mile south of Rockport, SR1 starts going right along the shore. Westport is about 7 miles south of Hardy.
Other than the part between Portland-Gresham and Woodland, WA, I drove pretty much that route in 2011. We had been visiting friends and family in Sandy and Salem, and went to a place well south of Westport between Point Arena and Gualala. If their trip had been some sort of GBCW suicide pact or a planned murder-suicide there are lots of places along I-5 where they could have plunged off a cliff or into Lake Shasta. There would have been even more along SR299 and US101 as they drove through the Coast Ranges. Why travel all those hundreds of miles to the obscure tiny town of Westport were suicide or murder-suicide their purpose?
SR1, starting around Hardy as noted above hugs the coast. It goes along cliff tops, low near the few large beaches and river/creek crossings. Parts of it are very winding, including up and down hill hairpin turns. It's not safe for the driver to be sight-seeing or distracted, and even more so at night (which is downright scary! BTDT). Which brings up another unknown. They were found early Monday afternoon, but SR1 isn't high traffic, and apparently their vehicle was not visible unless a viewer took that turn-out, which would be a low % of already sparse traffic. IOW it is not known when the cliff plunge happened, daylight, total dark, or morning dusk.
So ... suicide pact or murder-suicide? Possible, but why drive hundreds of miles to do it, even if they were familiar with CA's Mendocino County coast?
Accident? The 75-foot turn-out and lack of evidence of braking pretty much rules out a misjudged turn. But the driver being distracted is not impossible, and the driver having fallen asleep is very possible (the bodies of 3 of the children having been thrown clear or washed away, apparently, suggests that they had unfastened their seat belts and were asleep. Obviously I'm speculating.
At this point I think the investigation outside of the immediate scene and their vehicle is focused on reconstructing their route and timing. They're looking for witnesses and security footage from places along their route that show them getting gas and such.
