mid 70's 3colored dimming, brightening lights following Skagit River, Washington

My two brothers and I were playing outside, it was about 9-10 o'clock outside during summer months. My father came outdoors for us to come in right away and pointed to a circle flying from west to east following the skagit river. 
Our dog was barking, dad rushed us inside, locking the doors and closing the windows. He stood above the kitchen sink staring out the window. 
My brothers and I ran into the livingroom where we could also watch it. It was round, moved slowly and was red blue and yellow or white.  The glowing ball would gradually brighten then dim, change colors and the lights would contimue to dim and brighten then change. 
My father closed the curtains and we were ordered to stay in and stay totally away from the windows. 
Never heard another thing about it from anyone but the family. Has anyone else experienced this? I remember my father calling someone, he was very shaken
Date may be approximate, although the witness does not indicate that fact.  PD