How do spiders build webs so far between trees?

While hiking in a valley in King’s Canon in California in the 90s, I saw spider webs stretching across the valley from one mountain peak to another, way above my head. At first I thought I was seeing things. But the forest ranger confirmed I was seeing spider webs. He said they were gossamer spiders, which was probably just a term for spiders who seem to sail long distances on the wind currents. I felt lucky to have seen these gossamer webs!