SoCal (<34 deg N) has no artificial drainage in updated maps

See slides from May 12 HWP [dashboard update](https://drive.google.com/file/d/1QEyl8UPn6x1Hw51ZAMTJ2LvwvbDy3a4M/view?usp=sharing). I believe the next step is to determine the COMIDs of the SoCal catchments & subset the raw data for those catchments, and determine whether there are any subsurface tiles & field ditches estimated for these catchments/COMIDs.

Note: I am currently using the method from [Nakagaki 2016](https://www.sciencebase.gov/catalog/item/58d9dec6e4b0543bf7fda70e) for subsurface drainage. The one from [Wieczorek 2004 ](https://www.sciencebase.gov/catalog/item/57067469e4b03f95a075ad3e) yields a pretty undecipherable map.

Start by reviewing the linked May 12 HWP dashboard update and the repository's map and raw-data entry points. Determine the COMIDs for the SoCal catchments, subset the raw data, and check for estimated subsurface tiles and field ditches using the referenced drainage methods; done when the apparent absence of artificial drainage is explained or corrected in the updated maps.

Written by the indexing model from the issue text.