The highest and the lowest points of the contiguous United States are 130 kilometres apart.

Almost everyone travels California lengthways: San Diego to San Francisco, or the reverse, along the coast. It is the comfortable direction, because it runs with the grain of the ground. The interesting direction is across it.

01 A state made of strips

Geologists divide California into eleven regions, and nearly all of them are elongated and parallel to one another. Across the middle of the state, from west to east, the order is always the same: the ocean, the Coast Ranges, the Central Valley, the Sierra Nevada and the desert basin. The names change to the north and south; the logic does not.

The reason is the plate boundary that runs through the state. The San Andreas Fault and its associated system have spent millions of years shifting one block past the other, and that motion does not raise rounded mountains: it lines up long ridges and valleys along the direction of the slip. Seen from the air the fault is a straight scar across the landscape, with the creeks cut and offset where they cross it.

There is one striking exception, the Transverse Ranges in the south, which run east to west instead of north to south and stand out for exactly that reason on a physical map. But they are the anomaly that shows what the rule is.

02 The range is tilted

The Sierra Nevada is not a symmetrical range. It is a tilted block of crust: lifted along one edge and sloping away from the other, like a trapdoor. The consequence is easier to grasp from the air than from the ground.

On the west the range climbs in a ramp more than a hundred kilometres long, with rivers descending slowly and forests stacked by altitude. On the east it simply stops. From the floor of the Owens Valley, at about 1,200 metres, the ground reaches the 4,421 metres of Mount Whitney in a little over fifteen horizontal kilometres.

There is the explanation for the number in the headline. The highest point of the contiguous United States and the lowest point in North America are not close in spite of the geology: they are close because of it. The same stretching that dropped the basins to the east is what raised and tilted the block of the range. They are two sides of a single movement.

03 The valley with only one door

Between the range and the Coast Ranges lies a trough 720 kilometres long and between 64 and 97 wide: the Central Valley. It covers some 47,000 square kilometres, around 11 per cent of the state's surface, and it is so flat you can drive across it without registering a single gradient.

The peculiarity is not the shape but the drainage. The catchment feeding the valley covers some 160,000 square kilometres, more than a third of California, and all that water has one natural outlet to the sea: the Carquinez Strait, which carries it into San Francisco Bay and out to the Pacific. More than a third of the state drains through a single door.

That door also works in reverse. In the delta where the Sacramento and San Joaquin rivers meet, the canal network that sends water south begins, and that distribution is what carries the valley's farming. The result reads better from the air than on any map.

04 Behind the range, the shadow

East of the range the other California begins. The mountains intercept the moisture arriving from the Pacific, and what lies behind is rain shadow: closed basins with no outlet to the sea, where water comes in and leaves only by evaporating.

Badwater, in Death Valley, lies 85 metres below sea level and is the lowest point in North America. The white crust on the floor is not sand: it is the salt left by thousands of years of lakes that dried out with nowhere to drain.

It is the same water, told in three acts. It falls on the western slope, is stored as snow in the range and comes down into the Central Valley, where it is shared out. What never crosses the crest stays in the east and ends as a crust of salt.

05 Why this matters to a traveller

All of the above leads to a counter-intuitive recommendation. The coast is the California everyone knows, but it is only the first of five strips, and the narrowest of them.

A west-to-east run — coast, Coast Ranges, valley, range, desert — fits into a couple of days of driving and crosses five landscapes with nothing in common. The same time spent going down the coast covers considerably more kilometres and sees far less variety.

It is also worth reckoning with what the grain of the ground imposes. Crossing the range is only possible over a handful of passes, and the highest are closed by snow for much of the year, so the crossways route depends on the date in a way the lengthways route does not. California lets you travel along it almost without thinking. Across it, you have to plan.