Loose rock can collapse any time of the year. There was probably a small rock fall that caused WSDOT to inspect the site and call this team when additional loose rock was found.That was neat all kind of jobs out there.I take it this is performed to get ready for the rainy season?
There are similar nets along I-80 in the Sierra Nevada west of Donner Pass. There may be more east of the pass but I haven't noticed them.You can see the net rock fences on the PA Turnpike in the mountain sections. In a couple of places here in Virginny too. Kinda wonder how they clean the nets out. Really big vacuum?