What type of line is used when land grants were surveyed before March 17, 1840?

The type of line used when land grants were surveyed before March 17, 1840, is the highest high tide line. This refers to the highest point that the tide reaches along the shore and was often used as a boundary marker for land along coastal or tidal waters during that period.

Understanding the historical context is essential, as land surveying practices and legal definitions of boundaries have evolved over time. The highest high tide line serves as a natural and observable boundary that aligns with longstanding surveying practices prior to the establishment of more modern surveying regulations. During the era in question, surveyors relied on natural features, and the highest high tide line provided a practical and recognizable point for delineating property lines near coastal areas.

In contrast, the other options refer to different water-related boundaries or features that may not have been recognized in the same manner during the surveying practices of that time. Therefore, the correct line associated with land grants from that specific period is indeed the highest high tide line.