Pasadena orogeny is a mountain building event in the Western United States. Conventionally it refers to the formation of mountains in mainly Southern California during the Pleistocene and lasting until the present day; originally it referred to the uplift of the San Gabriel Mountains.

The Pasadena orogeny is a major Late Quaternary ^[1]-modern event ^[2] of mountain formation, ^[1] which took place in the middle or perhaps late Pleistocene ^[3] or to the present-day. ^[4] It is also known as the "Coast Ranges orogeny" ^[3] or considered to be part of the Cascadian orogeny ^[5] or Alpide Orogeny. ^[6] Finally, the term "Pasadena orogeny" is sometimes applied to all very recent orogenies around the Pacific Ocean. ^[7] The type location is close to Pasadena, California in the Transverse Ranges, ^[8] and originally referred to the fast rise of the San Gabriel Mountains recorded there. ^[9]

During this orogeny mountain ranges such as the San Bernardino Mountains, San Gabriel Mountains, San Jacinto Mountains, Santa Monica Mountains, Santa Ynez Mountains ^[10] and the Transverse Ranges grew, ^[11] as did the northern Channel Islands ^[10] such as Catalina Island and San Clemente Island, ^[12] the Kettleman Hills anticline in the San Joaquin Valley ^[13] and the Palos Verdes Hills. ^{[14] [12]} Sometimes the concept is limited to the uplift of the Transverse Ranges. ^[15]

The general uplift of mountains over a length of over 400 kilometres (250 mi) is caused by the collision of the North American Plate with other geologic structures that are attached to the Pacific Plate. ^[10] This orogeny has resulted in the uplift of mostly north-south trending mountain chains, although some east-west trending uplifts are also found such as the Channel Islands and the Transverse Ranges; ^[13] much of the uplift took place at the edge of basins. ^[16] The Pasadena orogeny is accompanied by earthquake activity, which includes tsunami hazards. ^[17]

Folding accompanying the uplift of the Coast Ranges in Southern California, ^[3] folding farther north at Morro Bay ^[18] and the structure of the Santa Barbara Basin ^[1] and Ventura Basin are consequences of the Pasadena orogeny. ^[4] The city of Long Beach, California lies within the affected region. ^[2]