Getting huge range of values when using Flow Accumulation tool in ArcGIS Desktop?

I’m trying to use ArcGIS Desktop to delineate watersheds for a series of sampling sites. I’ve been following the protocol laid out by WhiteboxDev in General steps to create watershed boundary in ArcGIS Spatial Analyst?

However, I’m having troubles with the flow accumulation tool. When I run it based on my flow direction raster, I end up with values that range from zero to nine million, which seems wrong, and can’t be used for the next steps.

Does anyone have an idea why this might be happening, and what I can do to fix it?

I haven’t used any other layers to weight the output, and I think my flow direction layer is accurate.

I’m using the NASA SRTM elevation data, which has 1 arc-second (~30 m) cells. In Arc, the cell dimensions are listed as (0.00027777778, 0.00027777778), which I assume is in degrees. I understand the idea of the flow accumulation tool, I just don’t understand why it’s skewing all of my data.