Not as popularly presented. I do see as logical there are ancient ultimate intelligent entities in our galaxy and universe, but more likely more inorganic like machines necessary to travel across vast regions of space.
An intelligent extraterrestrial organic entity with advanced technology that became marooned on Earth would certain have plenty of totally uninhabited natural lands along some areas of our West Coast to remain secretly hidden in it they had some way to eat consuming available vegetation or even deer and foul. Especially if they were able to monitor our electromagnetic communications. Would expect they would do so living underground in caves/tunnels, coming out during days when they would not be infrared trackable.