This document reviews the history, design, and use of the long-base laser strainmeters developed at IGPP/SIO since 1970: the longest-running and most stable examples of such instruments. We describe the principles of operation, limitations on dynamic range the frequency response, and major sources of error, along with the design and construction methods used. We also provide results on reliability of operation and the methods used to produce final high-quality data from what is recorded in the field: both based on close to 100 instrument-years of experience. We describe the setting of the two long-running instruments in California, at Pin~on Flat Observatory and at Durmid Hill; for both locations we summarize results on long-term strain, tidal strains, and various strain ``events'': the last almost all related to earthquakes, since the results of these high-quality measurements have shown few departures from steady strain accumulation with time.

The continuous GPS sites at Pin˜on Flat Observatory (PFO) (which are called, naturally, PIN1 and PIN2) are two of the oldest continuous GPS sites in southern California and are also the originals of the drilled-braced monument design now in wide use. They are unique in providing a long-term record between two closely-spaced monuments. Unfortunately that record, particularly in its earlier phases, is somewhat complicated because of many changes made in the systems used. Some of these changes were done as part of tests; others were unavoidable consequences of attempting to make continuous GPS measurements at a period (the early 1990’s) when the equipment available was much more cumbersome, and much more expensive, than later: the expense meant that a succession of equipment had to be borrowed from different sources in order to collect data continuously. This document describes these changes in a form more complete than the usual standardized GPS site logs allow, partly as backup to a paper giving results from an analysis of the baseline between these monuments (Agnew et al. 2005), which used the L1 and L2 signals separately to get higher precision. We refer to this as the ‘‘baseline’’ analysis. These sites have also been analyzed as part of the network analysis done routinely by the Scripps Orbit and Permanent Array Center (SOPAC) and by the Jet Propulsion Laboratory (JPL). Section 6.2 describes how the corrections given here can be applied to the SOPAC time series, and compare these to the offsets determined by SOPAC. Note that the SOPAC analysis makes use of a site history log; since this is a dynamic document, when we refer to this site history we mean the version of June 2004. Following our custom for most PFO projects, we maintained a detailed log of the construction of these monuments and, later, of various activities related to them. Appendix A has been compiled from these logs, omitting material about other sites and about issues, such as telemetry, that were important to keep track of at the time but which are unlikely to be of relevance in processing the data or understanding the results. In keeping these logs we preferred too much completeness rather than too little; but a consequence of this, and of the diary form used, is the difficulty of extracting an overview, so we provide that here.