witness post
n.— «In recent years the state of Louisiana has embarked on the grueling process of improving its infrastructure maps. People trudge through marshes looking for so-called witness posts, aboveground markers for pipelines. After one such study, notes Roland Guidry, Louisiana’s oil-spill coordinator, “some of the companies were flabbergasted that their pipelines were over a quarter of a mile off from where they thought.”» —“The next energy crisis” by Nicholas Varchaver Fortune/CNNMoney Aug. 2, 2007. (source: Double-Tongued Dictionary)