There is a photograph that I always think sums up my working relationship with the Guardian photographer Sarah Lee. It shows us standing in a boutique in California, trying on elaborate hats and posing in the mirror as sunlight streams through the windows. It was taken in the early spring of 2013, a few days after Sarah called me and asked if I’d be interested in walking the length of Sunset Boulevard with her. I immediately said yes, scrabbled for a ticket, and headed west with little thought of what I would write or where it belonged, only that I knew how much I wanted us to work together.

I like this picture because I remember the giddiness of that pit-stop, weary and dusty-footed somewhere along Sunset’s 24-mile schlep. I like to imagine that this is how people meet us when we work together: side by side, an odd but happily synchronated team. And because I look at this picture and think that this is where something special began.

That walk along Sunset grew into a larger project, where we walk the length of single streets through American cities. More recently it has led to a new photography-and-words project about the west coast of America and life around Santa Monica pier. We’ve called it West of West, and have collected it in a book that we’re now crowdfunding via the publisher Unbound.

Sarah and I have been working together since we started at the Guardian around the same time, and were sent on a succession of of illustrious assignments – from voxpops, fashion shoots, and interviews to the time I had to learn how to pole dance, to the afternoon we passed in an office cupboard while, for some reason I cannot now recall, I had to pretend to be on the telephone.

They were silly things then, but always made bearable by how much we laughed while doing them, and by the great understanding we had for one another. It’s rare that you find that immediate bond with someone. Since then we’ve fallen into a particular way of working together – somehow we have the same eye, the same rhythm, so that Sarah’s photographs are not a literal illustration of my words, and nor do my words describe her pictures; rather they speak to one another, as quietly inquisitive companions.

We discovered early on that we had a shared fascination with America – with its culture and its landscape and its people, and with what America and the west represent. We would talk about it at length on those walks along Sunset, Broadway, Pennsylvania, Calle Ocho and Woodward. We spoke about it again recently, about the openness, colour and light.

Sarah told me about the first time she visited California, almost 20 years ago now, when she was struck by the familiarity of “the way the light hits the asphalt, with the green signs on the freeway, because by the time you get there you’ve seen a thousand films”.

I liked that for Sarah the first impact was visual. For me, arrival in California was, and still is, a great sensory overload: the breadth of sky and weight of air, the scent of gasoline, and brickellbush, the rise of voices and bodies, all those echoes of literature and song. Perhaps because so much of what I have read and heard and seen in my life has been sewn with the narrative of the frontier, I can never quite shake the feeling that to reach this western point is both the culmination of a journey and the beginning of something new.

“The frontier is the line of most rapid and effective Americanisation,” said the historian Frederick Jackson Turner in a lecture he delivered at the Chicago World’s Fair of 1893 – a lecture that characterises much of the nation’s politics, history and storytelling, for America’s notion of itself. “American social development has been continually beginning over again on the frontier,” he said. “This perennial rebirth, this fluidity of American life, this expansion westward with its new opportunities, its continuous touch with the simplicity of primitive society, furnish the forces dominating American character …”

For many of us looking on from outside the US, Turner’s thoughts have been persuasive too. But in recent times, as the idea of American freedom has become muddied, the narrative seems more tangled and contradicted.

On the beach there is still a great levelling – all classes and colours seemingly united by the simple pleasures of shoreline, ocean, boardwalk and pier. By warm skin and soft sand, by the sweetness of the air.

It was some time before Sarah began photographing the area around Santa Monica pier, the long wooden structure that marks the endpoint of the historic Route 66 and, therefore, the great journey west, extending the idea of the frontier a good half-mile out into the Pacific Ocean.

“Starting to surf completely changed my relationship with that area,” Sarah told me recently. “You’re even wester of west when you’re surfing. The next stop is the great white shark breeding ground. You spend a lot of time looking back at the shore. You look along to Malibu and Point Dume. You see how the flights leave LAX and take off over the sea — an endless trail of planes shoot out and turn back eastward. You really do get a sense of it being the western point, that sense of it being the end of America, this whole continent. I can’t sit on the surfline and not think of my own journey out there.”

Back on land, she began to see the shore differently too: the blues and yellows and pinks of ocean, shore, sunset, as well as burger bar, bare skin, candyfloss. She began to see echoes “between the artificial landscape and the human landscape – in the way a pair of socks unintentionally matches the municipal topiary”, she says. “Or it’s the way the blue and yellow stripes on the cracked tarmac chime with the woman on the pier, wrapped in blue plastic, lost in thought and obviously living a tough life. It’s making connections all the time.”

“I think I see things more clearly when I have a camera and a sense of purpose,” she said. “This place that had become so important in my life, I wanted to look at it properly, closely. And it seemed the project just pulled into focus as I went along.”

Recently I found myself back in California, and one afternoon I walked along Santa Monica pier without Sarah; past the Bubba Gump Shrimp Co and the ferris wheel, the rock shop and the bait and tackle, out to where the air grows quieter. I turned my back on the ocean to watch the land, to see it pull into focus: the day’s light softening, the neon gathering, the couples entwined on the boardwalk, and the man slowly licking doughnut sugar from his fingers, and above them the young girl on her father’s shoulders, her small face fierce and bright and facing west.

• This article was corrected on 6 April 2018. Sarah Lee referred to Point Dume, not Point Doon, as stated in an earlier version.