Silver triangle shape - SilentI hesitated to report this, as we only saw this for a short time. We live in the Sierra Mountains about 4,200' elevation. Sitting at the table and looking due south thru a huge window, we saw a long silver triangle (jet or plane [?]) close at a low elevation. What is unusual is we live under a flight plan for Fresno - Las Vegas & back. These go north of our home. This craft appeared to be 1 mile or closer and low, almost equal with our elevation. At most I estimate it might have been 5,000'. It was headed west and when it tilted it was totally sleek from pointed nose to the tail which was completely straight across. No wings, just a very long thin triange shape. We ran to the west deck & couldn't see it anymore. Did our eyes deceive us? No noise.Possible fighter jet, w/no markings, but no noise.