Rita Graham’s Washington State encounter from Mysterious Monsters (1976). Dated to September 12, 1975, in the narration above, and to June 1975, according to the trailer’s narrator, below.

Washington State summary begins at 1:30 minute mark. End of trailer has a classic drive-in movie ad.

The Rita Graham incident in Mysterious Monsters (1976) reminds folks of the bathroom scene in The Legend of Boggy Creek (1972).

Of course, in The Abominable Snowman of the Himalayas, there is the tent encounter (starting at the 6:00 minute mark in the first clip below).

Released in 1957, it predates both of the 1970s’ scenes.  For its time, that Yeti movie was meant to scare the living daylights out of its audiences, as can be understood from the tone of the trailer at the bottom.

http://www.youtube.com/watch?v=010JEvQQwzo

The idea (and thus imagery) of a Yeti getting into a tent during a Nepalese expedition was a real fear for these explorers.