NORTHERN COAST RANGES REGION (A) 



This region is the northernmost of three arbitrary 

 subdivisions of the Coast Ranges limestone, dolomite, 

 and shell province. It encompasses all of the Coast 

 Ranges in Colusa, Del Norte, Glenn, Humboldt, Lake, 

 Mendocino, Tehama, Trinity, and Yolo Counties. The 

 region is flanked on the west by the Pacific Ocean, on 

 the east by the Sacramento \'alley, and on the 

 northeast by the Klamath Mountains (figure 1 and 

 plate 1 ) . A narrow strip of the northern Coast Ranges 

 extends northward into Oregon. The region is rather 

 sparsely populated, the largest city being Eureka with 

 28,137 people in 1960. The economy is based largely 

 on lumbering, recreation, agriculture, and fishing. In 

 general, the region is mountainous and many parts are 

 not easily accessible. Major transportation facilities 

 are limited by the north- and northwest-trending 

 ranges although most of the region is served by high- 

 way, rail, or port facilities. 



There are few limestone and no dolomite deposits 

 of economic interest even though occurrences of car- 

 bonate rock are common. Limestone has formed un- 

 der a variety of conditions since Late Jurassic time. 

 Perhaps the oldest limestone occurs as thin beds and 

 lenses in shale of the Knoxville Formation (Upper 

 Jurassic) exposed in the low hills of the Coast Ranges 

 that flank the Sacramento \'alley. Minor beds, lenses, 

 and concretions also are found in Cretaceous shales 

 that conformably overlie the Knoxville. Much of the 

 rest of the northern Coast Ranges is underlain by sedi- 

 mentary and volcanic rocks generally assigned to the 

 Franciscan Formation of Late Jurassic and Cretaceous 

 age. These rocks consist of gravwacke, chert, shale, 

 volcanic rocks, and minor amounts of limestone. Most 

 of the limestone is thin bedded, usually interstratified 

 with chert and commonly associated with altered vol- 

 canic rocks (greenstone). In a few cases, massive lime- 

 stone is associated mainly with graywacke of the 

 Franciscan Formation. 



Limestone that is more or less impure is found in 

 the marine Pullen Formation (Miocene and/or Plio- 

 cene) near Eureka and as lake beds or marls in the 

 Tehama and Cache Formations (Pliocene and/or 

 Pleistocene) that lie east of Clear Lake and along the 



western side of the Sacramento \'alley. In addition, 

 numerous surficial deposits of travertine, onyx mar- 

 ble, and calcareous tufa were formed in the vicinity of 

 mineral springs during Quaternary time. Beds of oys- 

 ter shells mav exist in the mud in modern or young 

 fossil bays along the coast although no such deposits 

 have been reported. 



About 10 deposits have been utilized for limestone 

 in the northern Coast Ranges. Total production is not 

 known Init probably does not exceed a few tens of 

 thousands of tons of limestone. Practically all of this 

 was used as agricultural limestone, to make lime for 

 construction use, and for mercury retorting. The only 

 deposit of sufficient size and purity to be of significant 

 economic interest is the F"ashauer Ranch deposit in 

 Mendocino (bounty. Some of the other deposits may 

 be of local use, particularly in road construction or for 

 agricultural purposes. Some of the travertine and 

 other surficial deposits, as well as the red limestone of 

 the Franciscan Formation, may be of interest as 

 sources of ornamental and architectural materials. 

 The red Franciscan limestone has been referred to as 

 the Lavtonville-type limestone and is described in de- 

 tail by Bailev ec al. (1964, p. 68-77) and Garrison and 

 Bailey (1967, p. B94-B100). 



The limestone deposits of the northern Coast 

 Ranges are shown on plate 1 A and are discussed below 

 in alphabetical order within each district. The dis- 

 tricts of the region are listed in geographic order from 

 north to south. 



HUMBOLDT DISTRICT (A-1) 



Minor amounts of limestone from the Richter, 

 Moore, and McC'lellan Ranch deposits have supplied 

 local agricultural needs at times in the past. Some lime 

 also was made at the Jacoby Creek deposit many years 

 ago. However, none of the known deposits is large 

 enough to be considered of significant future value. 



Hackett deposit. Location: N'/, sec. 16, T. 1 N., R. 

 1 \V ., H., 4', miles west-southwest of Rio Dell; Scotia 

 1 >-minutc quadrangle. Ownership: Mel Hackett, \'er- 

 non Hackett, et al., Rio Dell (196.?). 



