My initial guess would be a female black widow spider based on the markings.
After looking at other pictures, and comparing the color and shape of the hourglass, this may actually be a brown widow. It was also in a high traffic area, which is apparently more common with brown widows than blacks. This picture was taken of the spider upside down in its web, abdomen up.
Yes, my first thought was, “Brown Widow.” The orange hourglass seems to be fairly consistent in color within the species, Latrodectus geometricus. And,in this case, there is the easy clue that the Brown Widow is brown/blackish instead of totally black.