Cajalco is thought to be a Hispanic spelling of the word for "quail" in the languages of the Luiseño and Cahuilla who lived in the area.

[2] The word Cajalco is an acronym- California Jalisco Land Company of Los Angeles[3] Cajalco Canyon Creek originally flowed down the northeast face of the Gavilan Hills of the Temescal Mountains at 33°48′25″N 117°18′01″W / 33.80694°N 117.30028°W / 33.80694; -117.30028.

[4] It then turned northwest to take in waters from arroyos from Mead Valley and turned west down through the wide, gently sloping Cajalco Valley above Cajalco Canyon gathering waters from the Gavilan Plateau from Harford Spring Canyon at 33°50′04″N 117°21′42″W / 33.83444°N 117.36167°W / 33.83444; -117.36167, and from other minor arroyos.

It entered Temescal Wash at 33°49′24″N 117°30′16″W / 33.82333°N 117.50444°W / 33.82333; -117.50444 after descending through the steep narrow gorge of the Cajalco Canyon in the lower reach of the creek.

[7] Now the water of the upper reach of the creek flows down through Cajalco Valley to join this reservoir at 33°50′11″N 117°22′25″W / 33.83639°N 117.37361°W / 33.83639; -117.37361.