Вызов метода с ошибкой: "name 'structura_DB' could not be found" - C#

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.OleDb;
using System.Data.Odbc;
using System.Data.SqlClient;
 
namespace Excel_mod
{
    public struct structura_exl
    {
        public string SiteName;
        public string SiteID;
        public string DistrictID;
        public string DistrictName;
        public string ShchID;
        public string ShchName;
    }
 
    class Excel
    {
        public struct structura_DB
        {
            public string SiteName;
            public string SiteID;
            public string DistrictID;
            public string Site_qName;
            public string ShchID;
        }
 
        public List<structura_DB> FromDbase()
        {
            List<structura_DB> resDB = new List<structura_DB>();
            SqlConnection sqlConn = new SqlConnection("user id=sa;" +
                                          "password=1234;server=127.0.0.1;" +
                                          "Trusted_Connection=yes;" +
                                          "database=MainDB; " +
                                          "connection timeout=5");
 
            Console.WriteLine("*******Читаем из БД********");
 
            sqlConn.Open();
            SqlCommand sqlCmd = new SqlCommand();
            sqlCmd.Connection = sqlConn; 
            sqlCmd.CommandText = "select * from LOC_Sites_tmp";
            SqlDataReader dr = sqlCmd.ExecuteReader();

                while (dr.Read())
                {
                    structura_DB st_DB = new structura_DB();
                    st_DB.DistrictID = Convert.ToString(dr["District_ID"]);
                    st_DB.ShchID = Convert.ToString(dr["SHCH_ID"]);
                    st_DB.SiteID = Convert.ToString(dr["Site_ID"]);
                    st_DB.SiteName = Convert.ToString(dr["Site_Name"]);
                    st_DB.Site_qName = Convert.ToString(dr["Site_qName"]);
                    resDB.Add(st_DB);
 
                    Console.Write(st_DB.ShchID +" ");
                    Console.Write(st_DB.DistrictID + " ");
                    Console.Write(st_DB.SiteID + " ");
                    Console.Write(st_DB.SiteName + " ");
                    Console.Write(st_DB.Site_qName + " ");
                    Console.WriteLine(" ");
                    Console.WriteLine(" ");
                }
                return resDB;
        }
        
    }
     class Output
     {
        static void Main(string[] args)
        {
            Excel c1 = new Excel();
            List<structura_exl> resEx = c1.FromExl();
            List<structura_DB> resDB = c1.FromDbase();
            Console.ReadLine();
        }
     }
}