The slope is over 50 degrees at some point.
I made a quick pseudocolor rendering of the slope with QGIS using the global DEM from LRO LOLA. The slope was generated from the DEM using QGIS's slope tool, after having cropped the global DEM. Some artifacts (the vertical bands) can be seen though.
Also, Regional tiles from SLDEM2015 can be useful to not have ...
Like the answer from @Jack already noted, the confusion is indeed from comparing depth vs elevation.
What i really wanted to know was the depth below "sea level".
With Mars Trek's "Calculate Elevation Profile" tool you can find that the floor of Mojave crater is about 5.1 km below "sea level", 600 meters lower than Gale crater's !
Together with Nicholson ...