This is an adult in full breeding plumage. This species is a common migrant and winter visitor along the Pacific Coast. It is usually seen in marine environments where it favors deep water. This individual was apparently lost, spending several weeks in a golf course pond where it offered unusual opportunities for close-up photography. Compared to the similar Arctic Loon, Pacific Loon differs in its slightly smaller size, more rounded head, thinner bill, purple-glossed throat, narrower white stripes on neck sides, paler crown, and lack of a white flank patch. Canon PowerShot SX60 HS.
References:
del Hoyo, J., Collar, N. & Garcia, E.F.J. (2019). Pacific Loon (Gavia pacifica). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/467260 on 17 August 2019).
Russell, R. W. (2018). Pacific Loon (Gavia pacifica), version 1.2. In The Birds of North America (P. G. Rodewald, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bna.pacloo.01.2