Standing in groves of almond trees in perfectly regimented rows you could hear a pin drop. Not the chirp of a bird or the buzz of a bee. It was eerie. The distant sound of a helicopter broke the silence; an aerial crop-sprayer dousing the carpets of monoculture in every direction. The air smelt like washing up liquid; it caught in our throats and felt like it was creeping into our lungs.
We were witnessing what appeared to be a chemical assault on the landscape.
I was on a fact-finding mission with Sunday Times journalist, Isabel Oakeshott, for our book Farmageddon. How on a single trip, I thought, do I convince a hard-nosed journalist of the perils of industrial agriculture? The answer lay here in California; the land of milk and honey.
We learned how the local bees had gone; wiped out. Forty billion bees are instead trucked in from other states to pollinate the crops.
Taking to the sky in a small plane, we could see enormous stretches of the same crop patchworking the valley, broken by what seemed like vicious scars; mega-dairies - each with thousands of cows confined to muddy paddocks, with not a blade of grass in sight. We were flying over perhaps the biggest concentration of mega-dairies in the world. Yet there was no shortage of land; no logical reason for them not to be on grass.
Back in Britain, our countryside too is suffering the ravages of intensive farming; once common farmland birds like turtle doves, skylarks and tree sparrows have declined by up to 90%. Butterflies and bees too have declined, with less than a quarter of the bees needed to pollinate our crops.
Compared to the US, however, Britain and Europe are relative novices at the intensification game; but there is fresh impetus to intensify under the dubious justification of 'feeding the world', threatening to take our countryside and the quality of our food to a new tipping point. Some want to accelerate the industrialisation of farming in the name of 'sustainable intensification'. Without a change of tack, mega-dairies, 'battery'-reared beef and genetically engineered crops - and animals - will soon be the norm.
The system in the US wasn't even working for the farmers themselves. At a livestock market in a nearby town, a farmer wept as he told of how a friend's mega-dairy had gone out of business and the despairing owner took his own life.
A glimpse into a horrifying future. A warning. And we should take heed.
During three years of investigation for Farmageddon, I became struck by the link between how animals are kept and the quality of the food they produce. Generally, the more that animals are reared on the land with natural, varied diets, the healthier and tastier the food.
We instinctively know this, which is why terms like 'natural' and 'free-range' are so attractive. It also explains why marketers all too often try to mask factory-farmed food behind labels showing false depictions of green fields, small farmhouses accompanied by comforting terms like 'farm fresh' and 'country fresh'.
It made me angry at suggestions that factory farming is a 'necessary evil' to feed the poor. I question why is it right to expect people on low incomes to have to feed their children on unhealthy food? Do we really want a decimated countryside devoid of birds, bees and butterflies? And why isn't more fuss being made over the fact that enough grain to feed billions more people is being wasted through feeding it to industrially reared animals?
At a recent meeting with leading businesses someone asked what I would say to UK Prime Minister David Cameron if given three minutes to talk to him.
I would urge support for food production that puts animals back on the farm instead of in factories; extensive farming connected to the land, providing more nutritious food in ways that are better for the countryside and animal welfare. Government could help improve the health of the nation and safeguard future food supplies by building on natural resources: the pasturelands that cover a quarter of farmland worldwide, and two-thirds in Britain.
For a generation of consumers shielded from the realities of factory farming, brought up on picture-book images of Old Macdonald and his small farmyard idyll, reinforced by advertising and often misleading labels, the truth often comes as a shock. Putting farm animals back on the farm could be a big vote-winner too; many people mistakenly think it's where they are anyway!