The Atchison, Topeka and Santa Fe Railway had a number of spurs off their 2nd District mainline that ran northwards into the foothills of the San Gabriel mountains. These spurs, called the Foothill Spurs, faced challenging grades at times as they approached the foothills proper, and served a number of agricultural interests in the area, primarily orange and grape vineyards. Incidentally, these spurs also served packing houses and quarries along the way.
The Mission Vineyard Spur was one of these spurs, and branched from the Cucamonga Foothill Spur and headed west to Mission Vineyards.
See also The Upland Foothill Spur.