vanishing military fighter jet/s, saw was vastly high rate of speed at shockingly low altituide then vanished. in clear view

time and date were approximate to +- a few years, i could hear signifigant sound although not sustained, what i saw was from a clear vantage point across the line of sight and traveling from, west tp east. Aircraft speeding at a singular altituide near base of what i will call Tehachapie from Gorman in the west and towards the 14 Freeway going eastward. im guessing i watched the craft travelmore than 20 miles of horizontal distance my vantage point was at least 25 miles south from the described event and close to the 138 freway in the area known as Neenach. the most remarkable thing is that it was as if at some point the aircraft went into an opening within the lower portion off this mountain,,, a disporportionatley abrupt disaperance of the aircraft at what apeared to be a secret door opening and than closing near relative middle or lower elevation along the hill/mountain range {i presume it is in Kern County}
it was posibly tandem low flying jetcraft,,,, but they disssapeared suddenlly at high speed in broad daylingt. memory wants to tell me that i saw the mountainside swallow the fast moving jet craft. Logicaly these were of a military jetcraft in nature and capability.