Use the Mesh Tool.
The larger oval shape should be the contour of the Mesh element.
Then draw the inner oval shape with a spline.
Then select the Mesh, and SPACE-click the spline. A ridge will be added to the Mesh.
With the Mesh Tool active, you can click on any edge of of the Mesh contour or the ridge, and using the Pet Palette command, set the height of all points on that ridge in one step.
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