Good article from the SF Chronicle:

https://www.sfchronicle.com/bayarea/...g-16401921.php

The family was found at 11am Wednesday, but appears to have died sometime in the afternoon on Tuesday. Jonathan was found in a sitting position with his cell phone in his pocket, and holding the baby. The dog was near him. Ellen was a little further ahead, in the direction of the car. They seemed to be returning to the car when they died.

Some water was found on them, so it's unlikely they died of dehydration, especially all in the same spot, just 1.5 miles away from the car, and with water still with them. It was 107 degrees that day.

Because of the time that passed between their death and being found, it's unclear whether or not they went swimming.

What's perplexing investigatiors is that the two most likely explanations don't completely make sense. The carbon monoxide theory doesn't seem to add up given that they were all outdoors, and the toxic algae isn't known to cause death unless one ingests the water, and it seems hard to believe that all 3 humans would have drank enough tainted water to kill them, without noticing the bad color or taste.

The third possibility -- that it was a murder suicide through poisoning -- doesn't seem all that likely, since the family seemed happy, and in fact had just moved to the area to live out their dream of being close to nature. It didn't seem like anyone was depressed or in a rut. Both adults seemed happy and excited to be in their new town, and both seemed to really love the baby.

I think the guy being found in a sitting position is a clue, as was the direction they were moving. Something seems to have made everyone feel sick, and they were likely trying to get back to the car ASAP, especially given the hot weather which was probably making everything even more uncomfortable. Jonathan likely lost completely lost energy first, and sat down with the baby, telling his wife he wanted to rest. Perhaps both he and the baby died while sitting there, so she tried to leave the two of them to get to the car and save herself, and then she died a minute or so later. This could also explain why they all died so close together.

I could see that trail closing permanently if they never get an answer as to what happened.