all future requirements with a minimum of field work. Sufficient Pacific Southwest Region Reproduced from the holdings of the National Archives controls are available to replace destroyed stations and establish required new stations. A new station can be located by forming a strong triangle with any two of the adjusted primary stations. PRECISE ALIGNMENT An unusual feature of the survey program was ment of the 203 series satetions. This the alignment require- included measurement of a zero line to a linesr tolerance of not to exceed 1:25000 and establishing a 9000 foot line of sight to a tolerance of plus or minus one quarter inch. Vertical control for this alignment was accomplished by establishing a series of bench marks by precise differential leveling and applying a correction for curvature of the earth. Horizontal control stations were eStabdlished by night operations with precise equipment and procedures developed to produce the required accuracy. The alignment of the stations was accomplished by offset measurements from these controls established working point on each station. to a pre-