California TortiseShell Butterfly
Here is an article from the SF Gate:
Massive butterfly swarms becoming the talk of Tahoe
There aren't enough to block out the sun, but social media posts out of the Lake Tahoe area show enough swarming butterflies to get just about anyone who encounters them to pull over and start taking pictures.
While some think the butterflies are migrating monarchs — which have been declining at an alarming rate in California — the Reno Gazette-Journal identifies them as California tortoiseshell butterflies that are visiting the Sierra in search of the remnant of our winter snow pack.
The butterflies are known to frequent beaches and puddles in search of salt from the soil, according to the newspaper.
The bugs can be identified by their orange and red wings, and social media posts show them swarming in a few locations around the region".