Geothermal gradient near surface?
The trouble with geothermal gradients is they are not the same everywhere. It is generally accepted that the geothermal gradient is 25-30 °C/km but there can be local variations. In South Australia the gradient is generally 30° C/km, but in the deeper parts of the Cooper Basin the gradient is 55-60 °C/km. Elsewhere, at a depth of 200 ft the temp is 11 C. In the UK the average geothermal gradient is 26 °C/km, but locally it can be in excess of 35°C/km.
With near surface depths, the ground temperature will vary with depth according to the time of day.

So to get an accurate geothermal map for your region would require localized data.