PREFACE. 
Soon after Mr. Eldridge’s lamented death, June 29, 1905, an exam¬ 
ination was made of his unfinished reports on the oil fields of Cali¬ 
fornia to determine in what shape he left them. His field work had 
covered a period of approximately one year, from about July 1, 1901, 
to July 1, 1902. During this time he had examined all the principal 
oil districts from San Mateo County southward to the Santa Ana 
Mountains. He had planned to describe the oil fields of this entire 
area in one large monograph, and at the time of his death had prac¬ 
tically completed the manuscript and accompanying geologic maps for 
the chapters on the Parkfield (Monterey County), Santa Clara Valley 
(Ventura and Los Angeles counties), and Puente Hills (Los Angeles 
and Orange counties) districts. Poor health for some time previous 
to his death precluded his doing more than this, and although there 
were copious notes relating to all the other districts none of these 
had been written up. The sad duty of preparing the nearly com¬ 
pleted manuscript for publication and of utilizing the remaining 
notes for other reports was assigned to the writer. 
In order to facilitate the publication of the chapters nearest com¬ 
pletion it was deemed expedient to issue them one or more at a 
time as bulletins, instead of in a single monograph, as originally con¬ 
templated by Mr. Eldridge. This change in the method of publica¬ 
tion necessitated some changes in the arrangement of the text and 
the treatment of the subject. In making these alterations, however, 
it has been the writer’s sincere effort to modify as little as possible 
Mr. Eldridge’s style of writing and manner of presentation. 
The text and geologic maps of the Santa Clara Valley and Puente 
Hills reports are entirely the work of Mr. Eldridge, with the excep¬ 
tion of some changes in the arrangement and some minor additions 
bringing them up to date. The choice and preparation of the illus¬ 
trations and the preparation of the cross sections fell to the lot of 
the writer. The forbearance of the reader is besought for any 
inconsistencies or deficiencies in this bulletin, as they are doubtless 
largely due to the writer’s inability to interpret and transcribe the 
ideas which Mr. Eldridge recorded in his notes. 
Ralph Arnold. 
June 30, 1900. 
XI 
