Cartoon showing position of the slab. See data
The slab (purple line) begins with a shallow dive below Acapulco, then levels out almost to Mexico City. Below Mexico City it plunges steeply into the mantle and ends abruptly at a depth of about 500 km.
Note that active volcanoes occur above where the slab attains a depth of 100 km [Modified from Perez-Campos et al., GRL 2008].