San Antonio and Austin are around 80 miles apart and have nearly identical climates. But they are both about the same distance from the coast, which is probably the main driver of climate in TX.

The whole region is relatively flat swampy area, so probably moreso than in more mountainous places. The soil and vegetation is quite varied though.

Really? Assuming similar elevation, I'd expect the temperature of two points 60 miles apart on earth to average the same with fairly low standard deviation.

Is there something specific to your geography that leads you to assume the temperature 60 miles away wouldn't "be anywhere close to yours"?

In the San Francisco Bay Area, for example, the temperature commonly varies dramatically between some places which are a quarter mile apart. And one side of a hill can be persistently foggy while the other side is usually sunny.

That is true but it's also an infamously unusual aspect of the Bay Area.

Daly City never ceased to baffle me whenever I'd drive through from the valley to SF.

You sure? Thats the case for areas the size of entire states. You can look at any weather temperature map to prove this.

60 miles is the distance between downtown Seattle and the peak of Mt. Rainier. Downtown Tokyo to the peak of Mt. Fuji. The highest and lowest points in the contiguous US are Death Valley and Mt Whitney, only 80 miles apart, yes that's 20 more than 60 but you get the point here.

Even between places at roughly the same elevation, the climate can vary hugely within 60 miles of a coast. And a majority of the population of the US lives within 60 miles of a coast.

Plains vs mountains are way different biomes. In Texas you can drive 8 hours and maintain similar temps.

If they lived on a mountain, they probably wouldn't be attributing the weather difference to the urban heat island effect.

Its normal anywhere as long as you're not comparing coastal to non coastal, yes.

You can drive for an hour doing 70mph and still be within the Houston metro area.