Black triangle monolith passed over Longmont, Colorado, in the summer of 1978.

My girlfriend, at the time, and I wrer walking across Mian Street, in Longmont, Co., about mid afternoon.  Beautiful blue sky, no clouds at all!   
When suddenely the sky became dark, and I replied to my girlfriend, that it must be going to rain!  Her reply was for me to look up!   and how I'm able to describe of what she and I, and others saw with total amazement, was a dull looking black triangle, about 500ft. high,3-miles wide, and about 5-to 7 miles long.  It had hundreds of lights in straight rows underneath the craft. when the sun did actually shine on it,  it didn't appear to be glossy. 
It was high enough to clear the Rocky Mountains, right above the "Flatirons",  between Longmont and Boulder, Colorado.  As it passed over us, it did not make a sound at all!  
Viewing time was approximately 15min.  I can still remember as if it happened yesterday!
Witness indicates tht date in August 1978 is approximate.  PD