Final answer:
Metallica is the influential California Metal band that started in the 80's specializing in New Wave of British Heavy Metal covers, contrasting with the Pacific Northwest's grunge movement incubated in Seattle's unique music scene.
Step-by-step explanation:
The hugely influential California Metal band that got its start in the 80's as a cover band specializing in New Wave of British Heavy Metal songs is none other than Metallica. Emerging from the Los Angeles rock scene, they originally performed covers from British heavy metal bands, contributing to the unique sound development in California. Unlike the Seattle music scene, which incubated the grunge movement, California's focus was more towards glamor and image with bands like Poison exemplifying the 'Hair Metal' genre. Venues like The Whiskey A Go Go served as pivotal locations for bands to gain exposure and evolve the California hard rock and heavy metal music scene.