Small cloud becomes trapezoid shape and disappears

What appeared to be a small, darker cloud rising diagonally faster than normal clouds in the area became a trapezoidal shape with straight edges and faded into the background color. 
I would guess it was about thirty feet across.
((CORRESPONDENCE WITH SOURCE OF REPORT))
Night time, or daytime, sighting, please?  Was it 07:30 hrs., i.e. in the morning?
Thank you for the report!
Peter Davenport
NUFORC
((RESPONSE))
Yes, 0730 hrs. Weather was broken cumulus clouds 90% coverage at about 2000 AGL, 20 mile visibility. Temp probably around 56F. The way this object took on the color and texture of the background clouds was so impressive that I could not find words to tell the driver of my vehicle. 
Rarely am I speechless, but this event did it!
I am the ((deleted title--senior public employee)) for Ravalli County and a retired ((deleted title--senior public employee/position #2)), and ((deleted)) pilot...
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