Copy value & fill color and fill dynamically to last row of data

Okay this is just so simple, but I cannot figure out how to do it. I tried the macro recorder, and aside from the garbage it produced, it had a defined range. The macro should place the X in cell CG1 and add the background color, then fill down to the last row of data. If a "helper" column is needed to determine what the last row is, that would be column C.

1. I would like to use this macro for the Active worksheet (it will be used multiple times)
2. The # of rows is dynamic (based on the sheets as well as each week the amount of data varies)
3. The only content an X for the value in the cell and the fill color in Column CG
4. The color index is 44 (orange), which I believe is the same as this: .Color = 49407 (either can be used)

This is my recorded code. The macro works, the problem is the static range. This will not allow me to use it for multiple sheets, and the number of rows is different every week. Thanks in advance!

Sub test()

    Range("CG1").Select
    ActiveCell.FormulaR1C1 = "X"
    With Selection.Interior
        .Pattern = xlSolid
        .PatternColorIndex = xlAutomatic
        .Color = 49407
        .TintAndShade = 0
        .PatternTintAndShade = 0
    End With
    Selection.AutoFill Destination:=Range("CG1:CG6777")
    Range("CG1:CG6777").Select
    Range("CG1").Select
End Sub