Earlier datasets (1932-1977) are not available for use in area summaries and trend analyses because of concerns over the comparability of these datasets with later datasets (1984-present). The 1932 and 1956 are aerial imagery based. These datasets were classified into land and water categories via manual interpretation and some features were omitted as they fell beneath a minimum mapping unit. The 1973-1977 datasets are satellite imagery, however they are based off of imagery at a different resolution compared to the 1984-present imagery (60m vs. 30m). It is for these reasons that the earlier dates are not available for selection with these tools. While they can be informative at coarse, landscape and basin-level scales, we do not recommend using them in quantitative analysis at finer scales.