Multiple Detail Maps per Ramp Color

Hey all,

I'm trying to create a shader that will allow me to specify static texture maps for a certain alpha range in my heightmap. I already have a shader with a working ramp. Any suggestions? This is all I have so far:

Shader "TerrainTest - Vertex Lit" { Properties { _Heightmap ("Greyscale Heightmap(R) Alpha (A)", 2D) = "gray" {} _ColorRamp ("Colour Palette", 2D) = "gray" {} }

 SubShader 
 {
     Pass {
         Name "ColorReplacement"
         
         CGPROGRAM
             #pragma vertex vert
             #pragma fragment frag
             #pragma fragmentoption ARB_precision_hint_fastest
             #include "UnityCG.cginc"
             
             struct v2f
             {
                 float4    pos : SV_POSITION;
                 float2    uv : TEXCOORD0;
             }; 
             
             struct Input {
                 float2 uv_MainTex;
             };

             v2f vert (appdata_tan v)
             {
                 v2f o;
                 o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
                 o.uv = v.texcoord.xy;
                 return o;
             }
             
             sampler2D _Heightmap;
             sampler2D _ColorRamp;

             float4 frag(v2f i) : COLOR
             {
             // SURFACE COLOUR
                 float greyscale = tex2D(_Heightmap, i.uv).r;
             
             // RESULT
                 float4 result;
                 result.rgb = tex2D(_ColorRamp, float2(greyscale, 0.5)).rgb;
                 result.a = tex2D(_Heightmap, i.uv).a;
                 return result;
             }

         ENDCG
     }
     
 }

}