In "Logs", StimPlan averages the stress for each layer with zero local stress gradient. It is not able to calculate the local stress gradient automatically. When you transfer the stress log to "Geologic Layering", the single local stress gradient input will apply to every layer. Please see the two figures below. For example, if you input 0.7 psi/ft, each layer has the same local gradient of 0.7 psi/ft.

If the actual local stress gradient varies, you can always adjust the local gradient input in "Simulator Data --> Geologic Layering". As seen in the figure below, the sixth column is the local stress gradient. Also, you can use "Graphical Input" (as shown in the second figure below) to check if the local stress gradient aligns well with the stress logs.

For more information, please refer to StimPlan Help files named "Automatic Stress/Modulus Layering from Logs" and "Stress Gradient Input".