Welcome to Demolition Alley in Redwood National and State Parks, one of the more pulverized areas encountered while exploring with Chris Atkins. This may be a single-event clearing, where one burst of wind brought down the whole bunch. But it could have spanned several years. Chris is on a log in the lower left hand corner of the image for scale.
Several factors affect redwoods and whether they break or fall over, including soil saturation, protection from other redwoods and strength of wind gusts. The shape of a valley and where the redwoods grow can matter too. Thats why redwoods merely being the largest survivors known of their species does not mean they are genetically superior. It may be due to protection and what end of a valley they are in.
Imagine a garden hose for a moment. Have you ever seen the small tapering brass nozzles that cause a fast skinny jet of water? There's actually not much water volume flow through those nozzles. There is less water, but the shape causes a higher water velocity exiting the end. Now imagine wind entering the broad end of a valley, say 1500 feet wide, but the other end tapers to just 100 feet across. The shape of that valley can increase the wind velocity so that 100 mph winds entering, may become 150 mph exiting.
Anyhow, this is one of the largest clearings of blow-down we found exploring Redwood National and State Parks. Surely there are a few more out there.