The blue helicopters seen dropping materials off Reservoir Canyon Road east of the Cuesta Grade are part of a Pacific Gas and Electric Co. project to update its power lines that service San Luis Obispo and Atascadero.
The helicopters are currently laying equipment to set up for a routine upgrade project estimated to last through 2013.
The next helicopter drop is scheduled for Tuesday.
The utility will replace nearly 40 electric towers built in the 1920s, switch out 144 wood power poles with rust-prevented steel poles and re-conductor its existing 70-kilovolt power lines.
The goal is to ensure customers continue to receive reliable electricity service, PG&E spokesman Kory Raftery said.
The utility plans to build most of the towers this winter, so theyre ready for installation in summer and fall of 2012. The poles should also be switched out by the end of 2012.
The projects timeline is lengthy because PG&Es permit limits most work between Nov. 1 and April 31 as to not disturb red-legged frog habitats.
Motorist safety was also top-of-mind.
Signs have been posted in both directions of Highway 101 over the Cuesta Grade to notify the public that aerial work is taking place.
The helicopters also won't fly over the highway when they're carrying material or equipment.
The cost of the project wasn't immediately available Friday.