I wish to create a 3-Dimensional figure in either Adobe Illustrator of Photoshop that has a 2 curves in the foreground that transitions into a flat sheet along the z-axis. The 3-dimensional sheet that I've created (below, from Illustrator) has the two curves (and the downwarp) extruded across the entire sheet, but I was wondering if there is a relatively straight-forward way to gradually flatten towards the back of the sheet.
What I've done thus far: Made 2-D curved line, extruded the shape. I also tried the Warp function in Photoshop, but I couldn't get just the back of the 3D structure to be flat.
Thanks for your input.